# reticulate 1.37.0

- Interrupting Python no longer leads to segfaults.
  (#1601, fixed in #1602)

- Print method for Python callables now includes the callable’s signature.
  (#1605, #1607)

- Reticulate now installs successfully on Windows ARM64.
  (#1609, contributed by @andrjohns)

- `virtualenv_starter()` no longer warns when encountering broken symlinks.
  (#1598)

- Fixed issue where configuring reticulate `conda_*` functions 
  to use the executable `mamba` instead of `conda` was ignored.
  (#1608, contributed by @AlexandreGuinaudeau)

# reticulate 1.36.1

- Fix issue where `py_to_r()` method for Pandas DataFrames would error
  if `py_to_r()` S3 methods were defined for Pandas subtypes,
  (as done by {anndata}) (#1591).

- "Python Dependencies" vignette edits (@salim-b, #1586)

- Added an option for extra command-line arguments in
  `conda_create()` and `conda_install()` (#1585).

- Fixed issue where `conda_install()` would ignore user-specified
  channels during Python installation (#1594).

# reticulate 1.36.0

- Internal refactoring and optimizations now give a faster experience,
  especially for workflows that frequently access Python objects from R.
  For example, simple attribute access like `sys$path` is ~2.5x times faster, and
  a sample workload of `py_to_r(np_array(1:3) + np_array(1:3))` benchmarks
  ~3.5x faster when compared to the previous CRAN release.

- Fixed issue where callable python objects created with `convert = FALSE` would not be
  wrapped in an R function (#1522).

- Fixed issue where `py_to_r()` S3 methods would not be called on arguments supplied to
  R functions being called from Python (#1522).

- `install_python()` will now build optimized versions of Python on macOS and Linux (#1567)

- Default Python version installed by `install_python()` is now 3.10 (was 3.9) (#1574).

- Output of `reticulate::py_last_error()` now includes a hint, showing how to access
  the full R call stack (#1572).

- Fixed an issue where nested `py_capture_output()` calls result in a lost reference
  to the original `sys.stdout` and `sys.stderr`, resulting in no further visible output
  from Python, and eventually, a segfault. (#1564)

- Fixed issues reported by rchk, as requested by CRAN (#1581).

- `py_to_r(x)` now returns `x` unmodified if `x` is not a Python object,
  instead of signaling an error.

- New `as.data.frame()` method exported for Python Polars DataFrames (#1568)

- Fixed an issue where printing a delayed module (`import("foo", delay_load = TRUE)`)
  would output `<pointer: 0x0>`.

- `py_validate_xptr()` will now attempt to resolve delayed modules before
  signaling an error (#1561).

- R packages can now express multiple preferred Python environments to
  search for and use if they exist, by supplying a character vector to `import()`:
  `import("foo", delay_load = list(environment = c("r-foo", "r-bar")))` (#1559)

- Reticulate will no longer warn about ignored `use_python(,required = FALSE)` calls (#1562).

- `reticulate` now prefers using the agg matplotlib backend when the R session
  is non-interactive. The backend can also be overridden via the `MPLBACKEND` or
  `RETICULATE_MPLBACKEND` environment variables when necessary (#1556).

- `attr(x, "tzone")` attributes are (better) preserved when converting POSIXt to Python.
  POSIXt types with a non-empty `tzone` attr convert to a `datetime.datetime`,
  otherwise they convert to NumPy `datetime64[ns]` arrays.

- Fixed an issue where calling `py_set_item()` on a subclassed dict would
  not invoke a custom `__setitem__` method.

- `py_del_attr(x, name)` now returns `x` invisibly

- `source_python()` no longer exports the `r` symbol to the R global environment.
  (the "R Interface Object" that is used by Python code get a reference to the
  R `globalenv()`)

- Fixed hang encountered (sometimes) when attempting to call `iterate()`
  on an exhausted `py_iterator()` object multiple times (#1539).

- `iterate(simplify=TRUE)` rewritten in C for speed improvements (#1539).

- Update for Pandas 2.2 deprecation of `Index.format()` (#1537, #1538).

- Updates for CRAN R-devel (R 4.4) (#1554).

- Fixed an issue where `py_discover_config()` would discover `python` (v2) on the PATH
  in preference of `python3` on the PATH. (#1547)

- Fixed an issue where reticulate would error when using conda environments created
  with the (new) `conda env create` command. (#1535, #1543)

- Fixed an issue where reticulate would error when using a conda environment
  where the original conda binary that was used to create the environment
  is no longer available (#1555)

- Fixed an issue where a user would be unable to accept the prompt to create
  the default "r-reticulate" venv (#1557).

- `is_py_object()` is now exported (#1573).

# reticulate 1.35.0

- Subclassed Python list and dict objects are no longer automatically converted
  to R vectors. Additionally, the S3 R `class` attribute for Python objects is
  now constructed using the Python `type(object)` directly, rather than from the
  `object.__class__` attribute. See #1531 for details and context.

- R external pointers (EXTPTRSXP objects) now round-trip through
  `py_to_r(r_to_py(x))` successfully.
  (reported in #1511, fixed in #1519, contributed by @llaniewski).

- Fixed issue where `virtualenv_create()` would error on Ubuntu 22.04 when
  using the system python as a base. (#1495, fixed in #1496).

- Fixed issue where `csc_matrix` objects with unsorted indices could not be
  converted to a dgCMatrix. (related to #727, fixed in #1524, contributed by @rcannood).

- Added support for partially unexpanded variables like `$USER` in
  `XDG_DATA_HOME` and similar (#1513, #1514)

## Knitr Python Engine Changes:

- The knitr python engine now formats captured python exceptions to include the
  exception type and any exception notes when chunk options
  `error = TRUE` is set (reported in #1520, fixed in #1527).

- Fixed an issue where the knitr python engine would fail to include
  figures from python chunks if a custom `root.dir` chunk option was set.
  (reported in #1526, fixed in #1529)

- knitr engine gains the ability to save chunk figures in multiple files/formats
  (Contributed by @Rumengol in #1507)

- Fixed an issue where matplotlib figures generated in the initial chunk
  where matplotlib was first imported would be the wrong size
  (reported in #1523, fixed in #1530)

- Fixed an issue where the knitr engine would not correctly display altair
  compound charts if more than one were present in a document (#1500, #1532).

# reticulate 1.34.0

# reticulate 1.33.0

- Fixed issue where `asyncio`, (and modules that use `asyncio`), would error on
  Windows when running under RStudio (#1478, #1479).

- Added compatability with Python 3.12.

- `condaenv_exists()` is now exported.

# reticulate 1.32.0

- reticulate now supports casting R data.frames to Pandas data.frames using nullable
  data types, allowing users to preserve NA's from R atomic vectors. This feature is
  opt-in and can be enabled by setting the R option `reticulate.pandas_use_nullable_dtypes`
  to `TRUE`. (#1439)

- reticulate now exports a `chooseOpsMethod()` method, allowing for Ops dispatch
  to more specialized Ops methods defined for Python objects.

- `py_discover_config()` will now warn instead of error upon encountering a
  broken Python installation. (#1441, #1459)

- Fixed issue where Python would raise exception "OSError: [WinError 6] The handle is invalid"
  when opening a subprocess while running in Rstudio on Windows. (#1448, #518)

- Fixed issue where the multiprocessing Python module would crash or hang when spawning a
  `Process()` on Windows. (#1430, #1346, fixed in #1461)

- Fixed issue where `virtualenv_create()` would fail to discover a 'virtualenv' module
  in the system Python installation on Ubuntu. Reticulate will no longer discover
  and attempt to use the `venv` module stub present on Ubuntu systems
  where the `python3-venv` apt package has not been installed.
  (mlverse/pysparklyr#11, #1437, #1455)

- Fixed issue where the user was prompted to create an 'r-reticulate' venv
  in the RStudio IDE before reticulate was requested to initialize Python. (#1450, #1456)

- Improved error message when reticulate attempts to initialize a virtual environment
  after the Python installation it was created from is no longer available. (#1149, #1457)

- Improved error message on Fedora when attempting to create a virtual environment
  from the system python before running `dnf install python3-pip`.

- Fixed issue where `install_python()` on macOS in the RStudio IDE would fail to discover
  and use brew for Python build dependencies.

- Fixed error with `virtualenv_create(python = "/usr/bin/python")` on centos7. (#1467)

# reticulate 1.31

## Python Installation Management

- reticulate will no longer prompt users to install miniconda. Instead,
  reticulate will now prompt users to create a default `r-reticulate` venv.

- The search that reticulate conducts to select which Python installation to load
  has changed. See the updated Python "Order of Discover" in the "versions" vignette.
  `vignette("versions", package = "reticulate")`.

- Updated recommendations in the "python_dependencies" vignette for how R packages
  can approach Python dependency management.
  `vignette("python_dependencies", package = "reticulate")`

- New function `virtualenv_starter()`, which can be used to find a suitable
  python binary for creating a virtual environment. This is now the default
  method for finding the python binary when calling
  `virtualenv_create(version = <version>)`.

- `virtualenv_create()` and `virtualenv_install()` gain a `requirements` argument,
  accepting a filepath to a python requirements file.

- `virtualenv_create()` gains a `force` argument.

- `virtualenv_install()` gains a `python_version` argument, allowing users to customize
  which python version is used when bootstrapping a new virtual environment.

- Fixed an issue where the list of available python versions used by
  `install_python()` would be out-of-date.

- `install_python()` now gives a better error message if git is not installed.

- `install_python()` on macOS will now will use brew, if it's available, to install
   build dependencies, substantially speeding up python build times.

- New function `conda_search()`, contributed by @mkoohafkan in PR #1364.

## Language

- New `[` and `[<-` methods that invoke Python `__getitem__`, `__setitem__` and
  `__delitem__`. The R generics `[` and `[<-` now accept python-style slice
  syntax like `x[1:2:3]`. See examples in `?py_get_item`.

- `py_iterator()` gains a `prefetch` argument, primarily to avoid deadlocks
  where the main thread is blocked, waiting for the iterator, which is waiting
  to run on the main thread, as encountered in TensorFlow/Keras. (#1405).

- String columns from Pandas data frames containing `None`, `pd.NA` or `np.nan`
  are now simplified into character vectors and missing values replaced by `NA`
  (#1428).

- Converting from Pandas data frames containing columns with Pandas nullable
  data types are now correctly converted into R data.frames preserving the
  missing values (#1427).

## Knitr

- The knitr engine gains a `jupyter_compat` option, enabling
  reticulate to better match the behavior of Jupyter. When this chunk
  option is set to `TRUE`, only the return value from the last
  expression in a chunk is auto-printed.
  (#1391, #1394, contributed by @matthew-brett)

- The knitr engine now more reliably detects and displays matplotlib
  pending plots, without the need for a matplotlib artist object to be
  returned as a top-level expression. E.g., the knitr engine will now
  display plots when the matplotlib api returns something other than
  an artist object, (`plt.bar()`), or the matplotlib return value is
  not auto-printed due to being assigned, (`x = plt.plot()`), or
  suppressed with a `;`, (`plt.plot();`). (#1391, #1401, contributed
  by @matthew-brett)

- Fixed an issue where knitr engine would not respect chunk options
  `fig.width` / `fig.height` when rendering matplotlib plots. (#1398)

- Fixed an issue where the reticulate knitr engine would not capture output
  printed from python. (PR #1412, fixing #1378, #331)

## Miscellanous

- Reticulate now periodically flushes python `stdout` and `stderr` buffers even
  while the main thread is blocked executing Python code. Streaming output
  from a long-running Python function call will now appear in the R console
  while the Python function is still executing. (Previously, output might not
  appear until the Python function had finished and control of the main thread
  had returned to R).

- Updated sparse matrix conversion routines for compatibility with
  scipy 1.11.0.

- Fixed an issue where a py capsule finalizer could access the R API from
  a background thread. (#1406)

- Fixed issue where R would segfault (crash) in long-lived R sessions where both
  rpy2 and reticulate were in use (#1236).

- Fixed an issue where exceptions from reticulate would not be formatted properly
  when running tests under testthat (r-lib/rlang#1637, #1413).

- Fixed an issue where `py_get_attr(silent = TRUE)` would not return an R `NULL`,
  if the attribute was missing, as documented. (#1413)

- Fixed an issue where `py_get_attr(silent = TRUE)` would leave a python global
  exception set if the attribute was missing, resulting in fatal errors when
  running python under debug mode. (#1396)

# reticulate 1.30

- Fix compilation error on R 3.5. Bump minimum R version dependency to 3.5.

# reticulate 1.29

### Exceptions and Errors:

- R error information (call, message, other attributes) is now
  preserved as an R error condition traverses the R <-> Python boundary.

- Python Exceptions now inherit from `error` and `condition`, and can be
  passed directly to `base::stop()` to signal an error in R and raise an
  exception in Python.

- Raised Python Exceptions are now used directly to signal an R error.
  For example, in the following code, `e` is now an object that
  inherits from `python.builtin.Exception` as well as `error` and `condition`:
    ```r
    e <- tryCatch(py_func_that_raises_exception(),
                  error = function(e) e)
    ```
  Use `base::conditionCall()` and `base::conditionMessage()` to access
  the original R call and error message.

- `py_last_error()` return object contains `r_call`, `r_trace` and/or
  `r_class` if the Python Exception was raised by an R function called
  from Python.

- The hint to run `reticulate::py_last_error()` after an exception
  is now clickable in the RStudio IDE.

- Filepaths to Python files in the print output from `py_last_error()` are
  now clickable links in the RStudio IDE.

- Python exceptions encountered in `repl_python()` are now printed with the
  full Python traceback by default. In the RStudio IDE, filepaths in the tracebacks
  are rendered as clickable links. (#1240)

### Language:

- Converted Python callables gain support for dynamic dots from the rlang package.
  New features:
    - splicing (unpacking) arguments: `fn(!!!kwargs)`
    - dynamic names: `nm <- "key"; fn("{nm}" := value)`
    - trailing commas ignored (matching Python syntax): `fn(a, )` identical to `fn(a)`

- New Ops group generics for Python objects:
  `+`, `-`, `*`, `/`, `^`, `%%`, `%/%`, `&`, `|`, `!`, `%*%`.
  Methods for all the Ops group generics are now defined for Python objects. (#1187, #1363)
  E.g., this now works:
  ```r
  np <- reticulate::import("numpy", convert = FALSE)
  x <- np$array(1:5)
  y <- np$array(6:10)
  x + y
  ```

- Fixed two issues with R comparison operator methods
  (`==`, `!=`, `<`, `<=`, `>=`, `>`):
   - The operators no longer error on Python objects that define "rich comparison"
     Python methods that don't return a single bool. (e.g., numpy arrays).
   - The operators now respect the 'convert' value of the supplied Python objects.
     Note, this may be a breaking change as, e.g, `==`, may now no long return
     an R scalar logical if one of the Python object being compared was created
     with `convert = FALSE`. Wrap the result of the comparison with `py_bool()` to
     restore the previous behavior.
  (#1187, #1363)

- R functions wrapping Python callables now have formals matching
  those of the Python callable signature, enabling better
  autocompletion in more contexts (#1361).

- new `nameOfClass()` S3 method for Python types, enabling usage:
  `base::inherits(x, <python-type-object>)` (requires R >= 4.3.0)

- `py_run_file()` and `source_python()` now prepend the script directory to
  the Python module search path, `sys.path`, while the requested script is executing.
  This allows the Python scripts to resolve imports of modules defined in the
  script directory, matching the behavior of `python <script>` at the command line.
  (#1347)

### knitr:

- The knitr engine now suppresses warnings from Python code if
  `warning=FALSE` is set in the chunk options. (quarto-dev/quarto#125, #1358)

- Fixed issue where reticulate's knitr engine would attach comments in a
  code chunk to the wrong code chunk (requires Python>=3.8) (#1223).

- The knitr Python engine now respects the `strip.white` option (#1273).

- Fixed issue where the knitr engine would show an additional plot from a chunk
  if the user called `matplotlib.pyplot.show()` (#1380, #1383)

### Misc:

- `py_to_r()` now succeeds when converting subtypes of the built-in
  types (e.g. `list`, `dict`, `str`). (#1352, #1348, #1226, #1354, #1366)

- New `pillar::type_sum()` method now exported for Python objects. That ensures
  the full object class name is printing in R tracebacks and tibbles
  containing Python objects.

- `py_load_object()` gains a `convert` argument. If `convert = FALSE`,
  the returned Python object will not be converted to an R object.

- Fixed error `r_to_py()` with Pandas>=2.0 and R data.frames with a
  factor column containing levels with `NA`.

- `r_to_py()` now succeeds for many additional types of R objects.
  Objects that reticulate doesn't know how to convert are presented to
  the Python runtime as a pycapsule (an opaque pointer to the underlying
  R object). Previously this would error.
  This allows for R code to pass R objects that cannot be safely
  converted to Python through the Python runtime to other R code.
  (e.g, to an R function called by Python code). (#1304)

- reticulate gains the ability to bind to micromamba Python installations
  (#1378, #1176, #1382, #1379, thanks to Zia Khan, @zia1138)

- Default Python version used by `install_miniconda()` and friends
  is now 3.9 (was 3.8).


# reticulate 1.28

- Fixed issue where `source_python()` (and likely many other entrypoints)
  would error if reticulate was built with Rcpp 1.0.10. Exception and
  error handling has been updated to accommodate usage of `R_ProtectUnwind()`.
  (#1328, #1329).

- Fixed issue where reticulate failed to discover Python 3.11 on Windows. (#1325)

- Fixed issue where reticulate would error by attempting to bind to
  a cygwin/msys2 installation of Python on Windows (#1325).

# reticulate 1.27

- `py_run_file()` now ensures the `__file__` dunder is visible to the
  executing python code. (#1283, #1284)

- Fixed errors with `install_miniconda()` and `conda_install()`,
  on Windows (#1286, #1287, conda/conda#11795, #1312, #1297),
  and on Linux and macOS (#1306, conda/conda#10431)

- Fixed error when activating a conda env from a UNC drive on Windows (#1303).

# reticulate 1.26

- Fixed issue where reticulate failed to bind to python2. (#1241, #1229)

- A warning is now issued when reticulate binds to python2 that python2
  support will be removed in an upcoming reticulate release.

- `py_id()` now returns a character string, instead of an R integer (#1216).

- Fixed an issue where `py_to_r()` would not convert elements of a
  dictionary (#1221).

- Fixed an issue where setting `RETICULATE_PYTHON` or `RETICULATE_PYTHON_FALLBACK`
  on Windows to the pyenv-win `python.bat` shim would result in an error (#1263).

- Fixed an issue where `datetime.datetime` objects with a `tzinfo` attribute
  was not getting converted to R correctly (#1266).

- Fixed an issue where pandas `pandas.Categorical(,ordered=True)` Series were
  not correctly converted to an R ordered factor (#1234).

- The `reticulate` Python engine no longer halts on error for Python chunks
  containing parse errors when the `error=TRUE` chunk option is set. (#583)

- `install_python()` now leverages brew for python build dependencies like
  openssl@1.1 if brew is already installed and on the PATH, substantially speeding up
  `install_python()` on macOS systems with brew configured.

- Fixed an issue where reticulate would fail to bind to a conda environment on macOS or linux
  if conda installed a non-POSIX compliant activation script into the conda environment. (#1255)

- Fixed an issue where the python knitr engine would error when printing to
  HTML a constructor of class instances with a `_repr_html_` or `to_html` method
  (e.g., `pandas.DataFrame`; #1249, #1250).

- Fixed an issue where the python knitr engine would error when printing a
  plotly figure to an HTML document in some (head-less) linux environments (#1250).

- Fixed an issue where `conda_install(pip=TRUE)` would install packages into
  a user Python library instead of the conda env if the environment variable
  `PIP_USER=true` was set. `py_install()`, `virtualenv_install()`, and
  `conda_install()` now always specify `--no-user` when invoking `pip install`. (#1209)

- Fixed issue where `py_last_error()` would return unconverted Python objects (#1233)

- The Knitr engine now supports printing Python objects with
  `_repr_markdown_` methods. (via quarto-dev/quarto-cli#1501)

- `sys.executable` on Windows now correctly reports the path to the Python executable
  instead of the launching R executable. (#1258)

- The `sys` module is no longer automatically imported in `__main__` by reticulate.

- Fixed an issue on Windows where reticulate would fail to find Python installations from pyenv installed via scoop.

- Fixed an issue where `configure_environment()` would error on Windows. (#1247)

- Updated docs for compatibility with HTML5 / R 4.2.

- Updated r_to_py.sparseMatrix() method for compatibility with Matrix 1.4-2.

# reticulate 1.25

- Fixed an issue where reticulate would fail if R was running embedded under rpy2.
  reticulate now ensures the Python GIL is acquired before calling into Python.
  (#1188, #1203)

- Fixed an issue where reticulate would fail to bind to an ArcGIS Pro conda environment
  (#1200, @philiporlando).

- Fixed an issue where reticulate would fail to bind to an Anaconda
  base environment on Windows.

- All commands that create, modify, or delete a Python environment now echo
  the system command about to be executed. Affected:
    virtualenv_{create,install,remove}
    conda_{create,clone,remove,install,update}
    py_install

- `install_python()` and `create_virtualenv()` gain the ability to automatically
  select the latest patch of a requested Python version.
  e.g.: `install_python("3.9:latest")`, `create_virtualenv("my-env", version = "3.9:latest")`

- `install_python()` `version` arg gains default value of `"3.9:latest"`.
  `install_python()` can now be called with no arguments.

- Fixed an issue where reticulate would fail to bind to a conda python
  if the user didn't have write permissions to the conda installation (#1156).

- Fixed an issue where reticulate would fail to bind to a conda python if
  spaces were present in the file path to the associated conda binary (#1154).

- `use_python(, required = TRUE)` now issues a warning if the request will be ignored (#1150).

- New function `py_repr()` (#1157)

- `print()` and related changes (#1148, #1157):
  - The default `print()` method for Python objects now invokes `py_repr()` instead of `str()`.
  - All Python objects gain a default `format()` method that invokes `py_str()`.
  - `py_str()` default method no longer strips the object memory address.
  - `print()` now returns the printed object invisibly, for composability with `%>%`.

- Exception handling changes (#1142, @t-kalinowski):
  - R error messages from Python exceptions are now truncated differently to satisfy `getOption("warning.length")`.
    A hint to call `reticulate::py_last_error()` is shown if the exception message was truncated.

  - Python buffers `sys.stderr` and `sys.stdout` are now flushed when Python exceptions are raised.

  -`py_last_error()`:
    * Return object is now an S3 object 'py_error', includes a default print method.
    * The python Exception object ('python.builtin.Exception') is available as an R attribute.
    * Gains the ability to restore a previous exception if provided in a call `py_last_error(previous_error)`

  - Python traceback objects gain a default `format()` S3 method.

- Fixed `py_to_r()` for scipy matrices when scipy >= 1.8.0, since sparse matrices
    are now deprecated.

- Fixed `r_to_py()` for small scipy matrices.

- New maintainer: Tomasz Kalinowski

# reticulate 1.24

- Fixed an issue where `reticulate` would fail to bind to the system version
  of Python on macOS if command line tools were installed, but Xcode was not.

# reticulate 1.23

- `use_condaenv()` gains the ability to accept an absolute path to a python
  binary for `envname`.

- All python objects gain a `length()` method, that returns either `py_len(x)`,
  or if that fails, `as.integer(py_bool(x))`.

- `conda_create()` default for `python_version` changed from
  `NULL` to `miniconda_python_version()` (presently, 3.8).

- New function `py_bool()`, for evaluating Python "truthiness" of an object.

- `reticulate` gains the function `py_list_packages()`, and can be used to
  list the Python modules available and installed in a particular Python
  environment. (#933)

- `reticulate` now supports conversion of Python [datatable](https://github.com/h2oai/datatable)
  objects. (#1081)

- `repl_python()` gains support for invoking select magic and system commands
  like `!ls` and `%cd <dir>`. See `?repl_python()` for details and examples.

- The development branch for `reticulate` has moved to the "main" branch.

- `reticulate` gains `reticulate::conda_update()`, for updating the
  version of `conda` in a particular `conda` installation.

- `reticulate` gains `reticulate::miniconda_uninstall()`, for uninstalling
  the reticulate-managed version of Miniconda. (#1077)

- `reticulate::use_python()` and friends now assume `required = TRUE` by
  default. For backwards compatibility, when `use_python()` is called
  as part of a package load hook, the default value will instead be `FALSE`.

- `reticulate` now provides support for Python environments managed by
  [poetry](https://python-poetry.org/). For projects containing a
  `pyproject.toml` file, `reticulate` will attempt to find and use the virtual
  environment managed by Poetry for that project. (#1031)

- The default version of Python used for the `r-reticulate` Miniconda environment
  installed via `reticulate::install_miniconda()` has changed from 3.6 to 3.8.

- `reticulate::install_miniconda()` now prefers installing the latest
  arm64 builds of miniforge. See https://conda-forge.org/blog/posts/2020-10-29-macos-arm64/
  for more details.

- `reticulate::conda_create()` gains the `environment` argument, used when
  creating a new conda environment based on an exported environment definition
  (e.g. `environment.yml` or `environment.json`).

- `reticulate` gains the function, `conda_export()`, for exporting a conda
  environment definition as YAML. Environments are exported as via the
  `conda env export` command. (#779)

- `reticulate::find_conda()` will now locate miniforge Conda installations
  located within the default install locations.

- Fixed an issue that caused `reticulate::conda_install(pip = TRUE)`
  to fail on windows. (#1053, @t-kalinowski)


# reticulate 1.22

- Fixed a regression that caused `reticulate::conda_install(pip = TRUE)`
  to fail. (#1052)


# reticulate 1.21

- `use_condaenv("base")` can now be used to activate the base Anaconda
  environment.

- `reticulate` will now execute any hooks registered via
  `setHook("reticulate.onPyInit", <...>)` after Python has been initialized.
  This can be useful for packages that need to take some action after
  `reticulate` has initialized Python.

- Further refined interrupt handling.

- Fixed an issue where attempting to bind `reticulate` to `/usr/bin/python3`
  on macOS could fail if Xcode was not installed. (#1017)

- The `reticulate` Python REPL no longer exits when a top-level interrupt
  is sent (e.g. via Ctrl + C).

- The miniconda auto-installer now supports aarch64 Linux machines. (#1012)

- Fixed an issue where matplotlib plots were incorrectly overwritten when
  multiple Python chunks in the same R Markdown document included plot output.
  (#1010)

- `reticulate` can now use the version of Python configured in projects using
  [pipenv](https://pypi.org/project/pipenv/). If the project contains a
  `Pipfile` at the root directory (as understood by `here::here()`), then
  `reticulate` will invoke `pipenv --venv` to determine the path to the
  Python virtual environment associated with the project. Note that the
  `RETICULATE_PYTHON` environment variable, as well as usages of
  `use_python(..., force = TRUE)`, will still take precedence. (#1006)

- Fixed an issue where `reticulate::py_run_string(..., local = TRUE)` failed
  to return the dictionary of defined Python objects in some cases.


# reticulate 1.20

- Fixed an issue causing tests to fail on CRAN's M1mac machine.


# reticulate 1.19

- Fixed an issue where `reticulate`'s interrupt handlers could cause issues
  with newer versions of Python.

- `reticulate` now better handles Pandas categorical variables containing
  `NA` values. (#942)

- `reticulate` now supports converting `pandas.NA` objects into R `NA` objects.
  (#950)

- `reticulate` now sets the `PYTHONIOENCODING` environment variable to UTF-8
  when running within RStudio. This should allow UTF-8 input and output to be
  handled more appropriately.

- `reticulate` gains the `install_python()` function, used to install different
  versions of Python via [pyenv](https://github.com/pyenv/pyenv)
  ([pyenv-windows](https://github.com/pyenv-win/pyenv-win) on Windows).

- Interrupt signals (e.g. those generated by `Ctrl + C`) are now better handled
  by `reticulate`. In particular, when `repl_python()` is active, `Ctrl + C`
  can be used to interrupt a pending Python computation.

- `virtualenv_create()` gains the `pip_version` and `setuptools_version`
  arguments, allowing users to control the versions of `pip` and `setuptools`
  used when initializing the virtual environment. The `extra` argument can
  also now be used to pass arbitrary command line arguments when necessary.

- `virtualenv_create()` gains the `module` argument, used to control whether
  `virtualenv` or `venv` is used to create the requested virtual environment.

- `py_to_r.datetime.datetime` no longer errs when `tzname` is `NULL`, and
  instead assumes the time is formatted for `UTC`. (#876)

- `reticulate` now supports the rendering of [plotly](https://plotly.com/)
  plots and [Altair](https://altair-viz.github.io/) charts in rendered
  R Markdown documents. (#711)

- `reticulate` now avoids invoking property methods when inferring the type
  for Python class members, for auto-completion systems. (#907)

- `reticulate` now attempts to set the `QT_QPA_PLATFORM_PLUGIN_PATH`
  environment variable when initializing a Conda installation of Python,
  when that associated plugins directory exists. (#586)

- The `reticulate` Python engine now supports the `results = "hold"` knitr
  chunk option. When set, any generated outputs are "held" and then displayed
  after the associated chunk's source code. (#530)

- `conda_create()` gains the `python_version` argument, making it easier to
  request that Conda environments are created with a pre-specified version
  of Python. (#766)

- Fixed an issue where `reticulate::conda_install()` would attempt to
  re-install the default Python package, potentially upgrading or downgrading
  the version of Python used in an environment.

- Fixed an issue where `reticulate` invoked its `reticulate.initialized` hook
  too early.

- Fixed an issue where Python modules loaded on a separate thread could cause
  a crash. (#885)

- `conda_install()` now allows version specifications for the `python_version`
  argument; e.g. `conda_install(python_version = ">=3.6")`. (#880)

- Fixed an issue where `conda_install()` failed to pass along `forge` and
  `channel` in calls to `conda_create()`. (#878)

- Fixed an issue where Python's auto-loader hooks could fail when binding
  to a Python 2.7 installation.


# reticulate 1.18

- Fixed an issue where `python_config()` could throw an error when attempting
  to query information about a Python 2.6 installation.


# reticulate 1.17

- `reticulate` now checks for and disallows installation of Python packages
  during `R CMD check`.

- `reticulate` no longer injects the `r` helper object into the main
  module if another variable called `r` has already been defined.

- The function `py_help_handler()` has now been exported, to be used by
  front-ends and other tools which need to provide help for Python objects
  in different contexts. (#864)

- Fixed an issue where timezone information could be lost when converting
  Python datetime objects to R. (#829)

- Fixed an issue where numeric (rather than integer) dimensions could cause
  issues when converting SciPy sparse matrices to their R counterparts. (#844)

- Fixed an issue where R `data.frame`s with non-ASCII column names could not
  be converted to Pandas DataFrames. (#834)

- Fixed an issue where the `pip_ignore_installed` argument in `conda_install()`
  was silently being ignored.

- Fixed an issue where `reticulate::conda_install()` could re-install Python
  into an environment when not explicitly requested by the user.

- `reticulate` now sets `LD_LIBRARY_PATH` when discovering Python. (#836)

- `reticulate` is now better at capturing Python logger streams (those that
  write to stdout or stderr) when `py_capture_output()` is set. (#825)

- `reticulate` no longer calls `utils::loadhistory()` after each REPL iteration.

- `reticulate` now better detects when Python modules are loaded.

- `reticulate::import_from_path()` now accepts the `delay_load` parameter,
  allowing modules which should be loaded from a pre-specified path
  to be lazy-loaded.

- Fixed an issue where `reticulate` load hooks (normally defined via
  `setHook("reticulate::<module>::load", ...)`) would segfault if those
  hooks attempted to load the hooked module.

- `reticulate` now attempts to resolve the conda binary used to create the
  associated Conda environment in calls to `py_install()`. This should fix use
  cases where Conda environments are placed outside of the Conda installation
  itself.

- `reticulate` now sets `PYTHONPATH` before loading Python, to ensure modules
  are looked up in the same locations where a regular Python interpreter would
  find them on load. This should fix issues where `reticulate` was unable to
  bind to a Python virtual environment in some cases.

- `reticulate::virtualenv_create()` gains the `packages` argument, allowing one
  to choose a set of packages to be installed (via `pip install`) after the
  virtual environment has been created.

- `reticulate::virtualenv_create()` gains the `system_site_packages` argument,
  allowing one to control whether the `--system-site-packages` flag is passed
  along when creating a new virtual environment. The default value can be
  customized via the `"reticulate.virtualenv.system_site_packages"` option and
  now defaults to `FALSE` when unset.

- Fixed an issue where `reticulate::configure_environment()` would fail
  when attempting to configure an Anaconda environment. (#794)

- `reticulate` now avoids presenting a Miniconda prompt for interactive
  sessions during R session initialization.

- Fixed unsafe usages of `Rprintf()` and `REprintf()`.

- `reticulate::py_install()` better respects the `method` argument, when
  `py_install()` is called without an explicit environment name. (#777)

- `reticulate:::pip_freeze()` now better handles `pip` direct references.
  (#775)

- Fixed an issue where output generated from `repl_python()` would
  be buffered until the whole submitted command had completed.
  (#739, @randy3k)

- `reticulate` now explicitly qualifies symbols used from TinyThread
  with `tthread::`, to avoid issues with symbol conflicts during
  compilation. (#773)

- `reticulate` will now prefer an existing Miniconda installation over
  a `conda` binary on the PATH, when looking for Conda. (#790)


# reticulate 1.16

- TinyThread now calls `Rf_error()` rather than `std::terminate()`
  when an internal error occurs.

- Conversion of Pandas DataFrames to R no longer emits deprecation
  warnings with pandas >= 0.25.0. (#762)

- `reticulate` now properly handles the version strings returned by beta
  versions of `pip`. (#757)

- `conda_create()` gains the `forge` and `channel` arguments,
  analogous to those already in `conda_install()`. (#752, @jtilly)


# reticulate 1.15

- `reticulate` now ensures SciPy `csr_matrix` objects are sorted before
  attempting to convert them to their R equivalent. (#738, @paulofelipe)

- Fixed an issue where calling `input()` from Python with no prompt
  would fail. (#728)

- Lines ending with a semi-colon are no longer auto-printed in the
  `reticulate` REPL. (#717, @jsfalk)

- `reticulate` now searches for Conda binaries in /opt/anaconda and
  /opt/miniconda. (#713)

- The `conda` executable used by `reticulate` can now be configured using an R
  option. Use `options(reticulate.conda_binary = <...>)` to force `reticulate`
  to use a particular `conda` executable.

- `reticulate::use_condaenv()` better handles cases where no
  matching environment could be found. (#687)

- `reticulate` gains the `py_ellipsis()` function, used to access
  the Python `Ellipsis` builtin. (#700, @skeydan)

- `reticulate::configure_environment()` now only allows environment
  configuration within interactive R sessions, and ensures that the
  version of Python that has been initialized by Python is indeed
  associated with a virtual environment or Conda environment.
  Use `reticulate::configure_environment(force = TRUE)` to force
  environment configuration within non-interactive R sessions.

- `reticulate` now automatically flushes output written to Python's
  stdout / stderr, as a top-level task added by `addTaskCallback()`.
  This behavior is controlled with the `options(reticulate.autoflush)`
  option. (#685)

- `reticulate::install_miniconda()` no longer attempts to modify the
  system PATH or registry when installing Miniconda. (#681)

- `reticulate::conda_install()` gains the `channel` argument, allowing
  custom Conda channels to be used when installing Python packages.
  (#443)

- `reticulate::configure_environment()` can now be used to configure a
  non-Miniconda Python environment. (#682; @skeydan)

- Fixed an issue where matplotlib plots would be included using absolute
  paths, which fails in non-standalone documents rendered to HTML. (#669)

- Fixed an issue where `reticulate` would attempt to flush a non-existent
  stdout / stderr stream. (#584)


# reticulate 1.14

- Fixed an issue where `rmarkdown::render()` could fail when including
  matplotlib plots when `knit_root_dir` is set. (#645)

- `reticulate` now scans for Conda installations within the ~/opt folder,
  as per the updated installers distributed for macOS. (#661)

- Python classes can now be defined directly from R using the `PyClass()`
  function. (#635; @dfalbel)

- reticulate is now compatible with Python 3.9. (#630, @skeydan)

- Pandas DataFrames with a large number of columns should now be converted to
  R data.frames more quickly. (#620, @skeydan)

- Python loggers are now better behaved in the Python chunks of R Markdown
  documents. (#386)

- reticulate will now attempt to bind to `python3` rather than `python`,
  when no other version of Python has been explicitly requested by
  e.g. `use_python()`.

- reticulate now provides R hooks for Python's `input()` and `raw_input()`
  functions. It should now be possible to read user input from Python scripts
  loaded by reticulate. (#610)

- `reticulate` now more consistently normalizes the paths reported by
  `py_config()`. (#609)

- `reticulate` now provides a mechanism for allowing client packages to declare
  their Python package dependencies. Packages should declare the Python packages
  they require as part of the `Config/reticulate` field in their `DESCRIPTION` file.
  Currently, this only activated when using Miniconda; as the assumption is that
  users will otherwise prefer to manually manage their Python environments.
  Please see `vignette("python_dependencies")` for more details.

- `reticulate` will now prompt the user to create and use a
  [Miniconda](https://docs.conda.io/en/latest/miniconda.html) environment
  when no other suitable Python environment has already been requested. This
  should help ease some of the trouble in setting up a Python environment on
  different platforms. The installer code was contributed by @hafen, from the
  [rminiconda](https://github.com/hafen/rminiconda) package.

- Fixed an issue where `virtualenv_create(..., python = "<python>")` could
  fail to use the requested version of Python when `venv` is not installed.
  (#399)

- Fixed an issue where iterable Python objects could not be iterated with
  `iter_next()` due to a missing class. (#603)

- Fixed an issue where Conda environments could be mis-detected as
  virtual environments.

- R functions wrapping Python functions now inherit the formal arguments
  as specified by Python, making autocompletion more reliable.
  (#573, @flying-sheep)

- Fixed an issue where attempts to query Conda for environments could fail
  on Windows. (#576; #575; @dfalbel)

- Properly check for NULL keyword arguments in `call_r_function()`.
  (#562, @dfalbel)


# reticulate 1.13

- Fixed an issue where subsetting with `[.python.builtin.object` could
  fail when `convert = TRUE` is set on the associated Python object.
  (#554)

- Fixed an issue where the wrong definition of `[[.python.builtin.object`
  was being exported. (#554)

- `py_install()` now accepts `python_version`, and can be used
  if a particular version of Python is required for a Conda
  environment. (This argument is ignored for virtual environments.)
  (#549)

- Fixed an issue where reticulate could segfault in some cases
  (e.g. when using the `iterate()` function). (#551)

- It is now possible to compile `reticulate` with support for debug
  versions of Python by setting the `RETICULATE_PYTHON_DEBUG` preprocessor
  define during compilation. (#548)

- reticulate now warns if it did not honor the user's request to load a
  particular version of Python, as through e.g. `reticulate::use_python()`.
  (#545)

- `py_save_object()` and `py_load_object()` now accept `...` arguments. (#542)

- `py_install()` has been revamped, and now better detects
  available Python tooling (virtualenv vs. venv vs. Conda). (#544)

- reticulate now flushes stdout / stderr after calls to `py_run_file()` and
  `py_run_string()`.

- Python tuples are now converted recursively, in the same way that Python
  lists are. This means that the sub-elements of the tuple will be converted
  to R objects when possible. (#525, @skeydan)

- Python OrderedDict objects with non-string keys are now properly
  converted to R. (#516)

- Fixed an issue where reticulate could crash after a failed attempt
  to load NumPy. (#497, @ecoughlan)


# reticulate 1.12

- Fixed an issue where Python objects within Python lists would not be
  converted to R objects as expected.

- Fixed an issue where single-row data.frames with row names could not
  be converted. (#468)

- Fixed an issue where `reticulate` could fail to query Anaconda environment
  names with Anaconda 3.7.

- Fixed an issue where vectors of R Dates were not converted correctly. (#454)

- Fixed an issue where R Dates could not be passed to Python functions. (#458)


# reticulate 1.11.1

- Fixed a failing virtual environment test on CRAN.


# reticulate 1.11

- Fixed an issue where attempts to activate virtual environments created with
  virtualenv 16.4.1 would fail. (#437)

- Fixed an issue where conversion of Pandas Categorical variables to R objects
  would fail. (#389)

- Textual output generated when adding items to a matplotlib plot object
  are now suppressed.

- If the last statement in a Python chunk returns a matplotlib plot object,
  the plot will now be auto-shown as in other environments.

- The reticulate function help handler now returns function arguments for
  Python builtin functions.

- Top-level Python statements can now include leading indent when submitted
  with `repl_python()`.

- The current `matplotlib` figure is now cleared as each Python chunk in an
  R Markdown document is run.

- The `r` helper object (used for evaluating R code from Python) now better
  handles conversion of R functions. (#383)

- The `use_virtualenv()` function now understands how to bind to virtual
  environments created by the Python `venv` module.

- Reticulate better handles conversions of R lists to Python, and similarly,
  Python lists to R. We now call `r_to_py()` on each sub-element of an R list,
  and similarly, `py_to_r()` on each sub-element of a Python list.

- Reticulate now always converts R `Date` objects into Python `datetime`
  objects. Note that these conversions can be inefficient -- if you would
  prefer conversion to NumPy `datetime64` objects / arrays, you should convert
  your date to `POSIXct` first.

- Python chunks containing errors will cause execution to halt if 'error=FALSE'
  during render, conforming with the default knitr behavior for R chunks.

- The output of bare statements (e.g. `1 + 1`) is now emitted as output when using
  the reticulate Python engine.

- Remapping of Python output streams to be R can now be explicitly enabled
  by setting the environment variable `RETICULATE_REMAP_OUTPUT_STREAMS` to 1. (#335)

- Allow syntax errors in Python chunks with 'eval = FALSE' (#343)

- Avoid dropping blank lines in Python chunks (#328)

- Use "agg" matplotlib backend when running under RStudio Desktop (avoids
  crashes when attempting to generate Python plots)

- Add `as.character()` S3 method for Python bytes (defaults to converting using
  UTF-8 encoding)

- Add `py_main_thread_func()` for providing R callbacks to Python libraries that may
  invoke the function on a Python background thread.

- Add `py_to_r` S3 methods for Scipy sparse matrices: CSR to dgRMatrix, COO to
  dgTMatrix, and for all other sparse matrices, conversion via CSC/dgCMatrix.


# reticulate 1.10

- Output is now properly displayed when using the `reticulate` REPL with
  Windows + Python 2.7.

- Address memory protection issues identified by rchk

- Make variables defined using `%as%` operator in `with()` available after
  execution of the with block (same behavior as Python).

- Check for presence of "__module__" property before reading in `as_r_class()`

- Only update pip in `virtualenv_install()` when version is < 8.1

- Support converting Python `OrderedDict` to R

- Support for iterating all types of Python iterable

- Add `conda_python()` and `virtualenv_python()` functions for finding the
  python binary associated with an environment.


# reticulate 1.9

- Detect python 3 in environments where there is no python 2 (e.g. Ubuntu 18.04)

- Always call r_to_py S3 method when converting objects from Python to R

- Handle NULL module name when determining R class for Python objects

- Convert RAW vectors to Python bytearray; Convert Python bytearray to RAW

- Use importlib for detecting modules (rather than imp) for Python >= 3.4

- Close text connection used for reading Python configuration probe


# reticulate 1.8

- `source_python()` now flushes stdout and stderr after running the associated
  Python script, to ensure that `print()`-ed output is output to the console.
  (#284)

- Fixed an issue where logical R matrices would not be converted correctly to
  their NumPy counterpart. (#280)

- Fixed an issue where Python chunks containing multiple statements on the same
  line would be evaluated and printed multiple times.

- Added `py_get_item()`, `py_set_item()`, and `py_del_item()` as lower-level
  APIs for directly accessing the items of e.g. a Python dictionary or a Pandas
  DataFrame.

- Fix issue with Pandas column names that clash with built in methods (e.g. 'pop')

- Improve default `str()` output for Python objects (print `__dict__` if available)


# reticulate 1.7

- Improved filtering of non-numeric characters in Python / NumPy versions.

- Added `py_func()` to wrap an R function in a Python function with the same signature as that of the original R function.

- Added support for conversion between `Matrix::dgCMatrix` objects in R and `Scipy` CSC matrices in Python.

- `source_python()` can now source a Python script from a URL into R environments.

- Always run `source_python()` in the main Python module.

- `py_install()` function for installing Python packages into virtualenvs and conda envs

- Automatically create conda environment for `conda_install()`

- Removed `delay_load` parameter from `import_from_path()`


# reticulate 1.6

- `repl_python()` function implementing a lightweight Python REPL in R.

- Support for converting Pandas objects (`Index`, `Series`, `DataFrame`)

- Support for converting Python `datetime` objects.

- `py_dict()` function to enable creation of dictionaries based on lists of
  keys and values.

- Provide default base directory (e.g. '~/.virtualenvs') for environments
  specified by name in `use_virtualenv()`.

- Fail when environment not found with `use_condaenv(..., required = TRUE)`

- Ensure that `use_*` python version is satisfied when using `eng_python()`

- Forward `required` argument from `use_virtualenv()` and `use_condaenv()`

- Fix leak which occurred when assigning R objects into Python containers

- Add support for Conda Forge (enabled by default) to `conda_install()`

- Added functions for managing Python virtual environments (virtualenv)


# reticulate 1.5

- Remove implicit documentation extraction for Python classes

- Add `Library\bin` to PATH on Windows to ensure Anaconda can find MKL

- New `source_python()` function for sourcing Python scripts into R
  environments.


# reticulate 1.4

- Support for `RETICULATE_DUMP_STACK_TRACE` environment variable which can be set to
  the number of milliseconds in which to output into stderr the call stacks
  from all running threads.

- Provide hook to change target module when delay loading

- Scan for conda environments in system-level installations

- Support for miniconda environments

- Implement `eval`, `echo`, and `include` knitr chunk options for Python engine


# reticulate 1.3.1

- Bugfix: ensure single-line Python chunks that produce no output still
  have source code emitted.


# reticulate 1.3

- Use existing instance of Python when reticulate is loaded within an
  embedded Python environment (e.g. rpy2, rice, etc.)

- Force use of Python specified in PYTHON_SESSION_INITIALIZED (defined by rpy2)

- Define R_SESSION_INITIALIZED (used by rpy2)

- Force use of Python when `required = TRUE` in `use_python` functions

- Force use of Python specified by RETICULATE_PYTHON

- `dict`: Don't scan parent frame for Python objects if a single unnamed list
  is passed.

- Wait as long as required for scheduling generator calls on the main thread

- Refine stripping of object addresses from output of `py_str()` method

- Added `py_id()` function to get globally unique ids for Python objects

- Added `py_len()` function and S3 `length()` method for Python lists (already
  had `length()` methods for dicts, tuples, and NumPy arrays).

- Exported `py` object (reference to Python main module)

- Added `eng_python()` (knitr engine for Python chunks)

- Improved compatibility with strings containing high unicode characters
  when running under Python 2

- Remove `dim` methods for NumPy arrays (semantics of NumPy reshaping are
  different from R reshaping)

- Added `array_reshape` function for reshaping R arrays using NumPy (row-major)
  semantics.

- Provide mechanism for custom R wrapper objects for Python objects

- Added interface to pickle (`py_save_object()` and `py_load_object()`)

- Catch and print errors which occur in generator functions

- Write using Rprintf when providing custom Python output streams
  (enables correct handling of terminal control characters)

- Implement `isatty` when providing custom Python output streams


# reticulate 1.2

- Add `np_array` function for creating NumPy arrays and converting the data type,
  dimensions, and in-memory ordering of existing NumPy arrays.

- Add `dim` and `length` functions for NumPy arrays

- Add `py_set_seed` function for setting Python and NumPy random seeds.

- Search in additional locations for Anaconda on Linux/Mac

- Improved support for UTF-8 conversions (always use UTF-8 when converting from
  Python to R)

- Ignore private ("_" prefixed) attributes of dictionaries for .DollarNames

- Provide "&#96;function&#96;" rather than "function" in completions.

- Fail gracefully if call to conda in `conda_list` results in an error

- Add `pip_ignore_installed` option to `conda_install` function.


# reticulate 1.1

- Allow `dict()` function to accept keys with mixed alpha/numeric characters

- Use `conda_list()` to discover conda environments on Windows (slower but
  much more reliable than scanning the filesystem)

- Add interface for registering F1 help handlers for Python modules

- Provide virtual/conda env hint mechanism for delay loaded imports


# reticulate 1.0

- Search WORKON_HOME (used by virtualenv_wrapper) for Python environments

- Support `priority` field for delay loaded modules.

- Use json output from conda_list (handle spaces in path of conda env)

- Look for callable before iterable when converting Python objects to R

- Correct propagation of errors in R functions called from Python

- Support for generators (creating Python iterators from R functions)

- Changed default `completed` value for `iter_next()` to `NULL` (was `NA`)

- Support for converting 16-bit floats (NPY_HALF) to R

- Don't throw error when probing Python <= 2.6

- Copy Python dictionary before converting to R named list (fixes issue
  with dictionaries that are mutated during iteration, e.g. sys.modules)

- Ensure that existing warning filters aren't reset by py_suppress_warnings


# reticulate 0.9

- Detect older versions of Anaconda during registry scanning.

- Don't probe python versions on windows when no executable is found

- Poll for interrupts every 500ms rather than 100ms

- Provide sys.stdout and sys.stderr when they are None (e.g. in R GUI)

- Add Scripts directory to PATH on Windows

- Add iter_next function for element-by-element access to iterators

- Eliminate special print method for iterators/generators

- Added `py_help()` function for printing documentation on Python objects

- Added `conda_version()` function.

- Search `dict()` parent frames for symbols; only use symbols which inherit
  from python.builtin.object as keys.


# reticulate 0.8

- Add `import_from_path()` function for importing Python modules from
  the filesystem.

- Add `py_discover_config()` function to determine which versions of Python
  will be discovered and which one will be used by reticulate.

- Add `py_function_docs()` amd `py_function_wrapper()` utility functions for
  scaffolding R wrappers for Python functions.

- Add `py_last_error()` function for retrieving last Python error.

- Convert 0-dimension NumPy arrays (scalars) to single element R vectors

- Convert "callable" Python objects to R functions

- Automatically add Python bin directory to system PATH for consistent
  version usage in reticulate and calls to system

- Added `length()` method for tuple objects

- Enable specification of `__name__` for R functions converted to
  Python functions.

- Give priority to the first registered delay load module (previously
  the last registered module was given priority)

- Add additional safety checks to detect use of NULL xptr objects
  (i.e. objects from a previous session). This should mean that S3
  methods no longer need to check whether they are handling an xptr.

- Added `py_eval()` function for evaluating simple Python statements.

- Add `local` option to `py_run_string()` and `py_run_file()`. Modify
  behavior to return local execution dictionary (rather than a reference
  to the main module).

- Use `PyImport_Import` rather than `PyImport_ImportModule` for `import()`

- Added ability to customize mapping of Python classes to R classes via
  the `as` argument to `import()` and the `register_class_filter()` function

- Added separate `on_load` and `on_error` functions for `delay_load`

- Scan customary root directories for virtualenv installations

- Allow calling `__getitem__` via `[[` operator (zero-based to match
  Python style indexing)

- Added `conda_*` family of functions for using conda utilities from
  within R.

- Implement comparison operators (e.g. `==`, `>=`, etc.) for Python objects

- Implement `names()` generic for Python objects

- Improve performance for marshalling of large Python dictionaries and
  iterators that return large numbers of items.

- Implement `str` methods for Python List, Dict, and Tuple (to prevent
  printing of very large collections via default `str` method)

- Use `grepl()` rather than `endsWith()` for compatibility with R <= 3.2

- Use `inspect.getmro` rather than `__bases__` for enumerating the base classes
  of Python objects.

- Fix `PROTECT`/`UNPROTECT` issue detected by CRAN

- Correct conversion of strings with Unicode characters on Windows

- Fix incompatibility with system-wide Python installations on Windows

- Fix issue with Python dictionary keys that shared names with
  primitive R functions (don't check environment inheritance chain
  when looking for dictionary key objects by name).

- Propagate `convert` parameter for modules with `delay_load`


# reticulate 0.7

- Initial CRAN release
