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https://github.com/instagram/MonkeyType

A Python library that generates static type annotations by collecting runtime types
https://github.com/instagram/MonkeyType

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A Python library that generates static type annotations by collecting runtime types

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README 

        
MonkeyType

==========



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MonkeyType collects runtime types of function arguments and return values, and

can automatically generate stub files or even add draft type annotations

directly to your Python code based on the types collected at runtime.



Example

-------



Say ``some/module.py`` originally contains:



.. code:: python



  def add(a, b):

      return a + b



And ``myscript.py`` contains:



.. code:: python



  from some.module import add



  add(1, 2)



Now we want to infer the type annotation of ``add`` in ``some/module.py`` by

running ``myscript.py`` with ``MonkeyType``. One way is to run:



.. code:: bash



  $ monkeytype run myscript.py



By default, this will dump call traces into a SQLite database in the file

``monkeytype.sqlite3`` in the current working directory. You can then use the

``monkeytype`` command to generate a stub file for a module, or apply the type

annotations directly to your code.



Running ``monkeytype stub some.module`` will output a stub:



.. code:: python



  def add(a: int, b: int) -> int: ...



Running  ``monkeytype apply some.module`` will modify ``some/module.py`` to:



.. code:: python



  def add(a: int, b: int) -> int:

      return a + b



This example demonstrates both the value and the limitations of

MonkeyType. With MonkeyType, it's very easy to add annotations that

reflect the concrete types you use at runtime, but those annotations may not

always match the full intended capability of the functions. For instance, ``add``

is capable of handling many more types than just integers. Similarly, MonkeyType

may generate a concrete ``List`` annotation where an abstract ``Sequence`` or

``Iterable`` would be more appropriate. MonkeyType's annotations are an

informative first draft, to be checked and corrected by a developer.



Motivation

----------



Readability and static analysis are the primary motivations for adding type

annotations to code. It's already common in many Python style guides to

document the argument and return types for a function in its docstring;

annotations are a standardized way to provide this documentation, which also

permits static analysis by a typechecker such as `mypy`_.



For more on the motivation and design of Python type annotations, see

:pep:`483` and :pep:`484`.



.. _mypy: http://mypy.readthedocs.io/en/latest/



Requirements

------------



MonkeyType requires Python 3.9+ and the `libcst`_ library (for applying type

stubs to code files). It generates only Python 3 type annotations (no type

comments).



Installing

----------



Install MonkeyType with `pip`_:



.. code:: bash



  pip install MonkeyType



How MonkeyType works

--------------------



MonkeyType uses the `sys.setprofile`_ hook provided by Python to interpose on

function calls, function returns, and generator yields, and record the types of

arguments / return values / yield values.



It generates `stub files`_ based on that data, and can use `libcst`_ to apply those

stub files directly to your code.



.. _pip: https://pip.pypa.io/en/stable/

.. _libcst: https://pypi.python.org/pypi/libcst

.. _sys.setprofile: https://docs.python.org/3/library/sys.html#sys.setprofile

.. _stub files: https://mypy.readthedocs.io/en/latest/getting_started.html#library-stubs-and-typeshed



.. end-here



See `the full documentation`_ for details.



.. _the full documentation: http://monkeytype.readthedocs.io/en/latest/



Troubleshooting

---------------



Check if your issue is mentioned in `the frequently asked questions`_ list.



.. _the frequently asked questions: http://monkeytype.readthedocs.io/en/stable/faq.html



Development

-----------



See `CONTRIBUTING.rst`_ for information on developing and contributing to MonkeyType.



.. _CONTRIBUTING.rst: https://github.com/Instagram/MonkeyType/blob/master/CONTRIBUTING.rst



LICENSE

-------



MonkeyType is BSD licensed.