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Fixes #116.
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Typeguard | ||
========= | ||
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.. contents:: | ||
:local: | ||
.. include:: ../README.rst | ||
:end-before: See the | ||
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Quick links | ||
----------- | ||
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.. toctree:: | ||
:maxdepth: 1 | ||
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userguide | ||
api | ||
versionhistory | ||
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Using type checker functions | ||
---------------------------- | ||
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Two functions are provided, potentially for use with the ``assert`` statement: | ||
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* :func:`~typeguard.check_argument_types` | ||
* :func:`~typeguard.check_return_type` | ||
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These can be used to implement fine grained type checking for select functions. | ||
If the function is called with incompatible types, or :func:`~typeguard.check_return_type` is used | ||
and the return value does not match the return type annotation, then a :exc:`TypeError` is raised. | ||
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For example:: | ||
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from typeguard import check_argument_types, check_return_value | ||
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def some_function(a: int, b: float, c: str, *args: str) -> bool: | ||
assert check_argument_types() | ||
... | ||
assert check_return_value(retval) | ||
return retval | ||
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When combined with the ``assert`` statement, these checks are automatically removed from the code | ||
by the compiler when Python is executed in optimized mode (by passing the ``-O`` switch to the | ||
interpreter, or by setting the ``PYTHONOPTIMIZE`` environment variable to ``1`` (or higher). | ||
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.. note:: This method is not reliable when used in nested functions (i.e. functions defined inside | ||
other functions). This is because this operating mode relies on finding the correct function | ||
object using the garbage collector, and when a nested function is running, its function object | ||
may no longer be around anymore, as it is only bound to the closure of the enclosing function. | ||
For this reason, it is recommended to use ``@typechecked`` instead for nested functions. | ||
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Using the decorator | ||
------------------- | ||
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The simplest way to type checking of both argument values and the return value for a single | ||
function is to use the ``@typechecked`` decorator:: | ||
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from typeguard import typechecked | ||
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@typechecked | ||
def some_function(a: int, b: float, c: str, *args: str) -> bool: | ||
... | ||
return retval | ||
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@typechecked | ||
class SomeClass: | ||
# All type annotated methods (including static and class methods) are type checked. | ||
# Does not apply to inner classes! | ||
def method(x: int) -> int: | ||
... | ||
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The decorator works just like the two previously mentioned checker functions except that it has no | ||
issues with nested functions. The drawback, however, is that it adds one stack frame per wrapped | ||
function which may make debugging harder. | ||
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When a generator function is wrapped with ``@typechecked``, the yields, sends and the return value | ||
are also type checked against the :class:`~typing.Generator` annotation. The same applies to the | ||
yields and sends of an async generator (annotated with :class:`~typing.AsyncGenerator`). | ||
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.. note:: | ||
The decorator also respects the optimized mode setting so it does nothing when the interpreter | ||
is running in optimized mode. | ||
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Using the profiler hook | ||
----------------------- | ||
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.. deprecated:: 2.6 | ||
Use the import hook instead. The profiler hook will be removed in v3.0. | ||
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This type checking approach requires no code changes, but does come with a number of drawbacks. | ||
It relies on setting a profiler hook in the interpreter which gets called every time a new Python | ||
stack frame is entered or exited. | ||
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The easiest way to use this approach is to use a :class:`~typeguard.TypeChecker` as a context | ||
manager:: | ||
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from warnings import filterwarnings | ||
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from typeguard import TypeChecker, TypeWarning | ||
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# Display all TypeWarnings, not just the first one | ||
filterwarnings('always', category=TypeWarning) | ||
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# Run your entire application inside this context block | ||
with TypeChecker(['mypackage', 'otherpackage']): | ||
mypackage.run_app() | ||
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Alternatively, manually start (and stop) the checker:: | ||
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checker = TypeChecker(['mypackage', 'otherpackage']) | ||
checker.start() | ||
mypackage.start_app() | ||
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The profiler hook approach has the following drawbacks: | ||
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* Return values of ``None`` are not type checked, as they cannot be distinguished from exceptions | ||
being raised | ||
* The hook relies on finding the target function using the garbage collector which may make it | ||
miss some type violations, especially with nested functions | ||
* Generator yield types are checked, send types are not | ||
* Generator yields cannot be distinguished from returns | ||
* Async generators are not type checked at all | ||
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.. hint:: Some other things you can do with :class:`~typeguard.TypeChecker`: | ||
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* Display all warnings from the start with ``python -W always::typeguard.TypeWarning`` | ||
* Redirect them to logging using :func:`logging.captureWarnings` | ||
* Record warnings in your pytest test suite and fail test(s) if you get any | ||
(see the `pytest documentation`_ about that) | ||
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.. _pytest documentation: http://doc.pytest.org/en/latest/warnings.html#assertwarnings | ||
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Using the import hook | ||
--------------------- | ||
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The import hook, when active, automatically decorates all type annotated functions with | ||
``@typechecked``. This allows for a noninvasive method of run time type checking. This method does | ||
not modify the source code on disk, but instead modifies its AST (Abstract Syntax Tree) when the | ||
module is loaded. | ||
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Using the import hook is as straightforward as installing it before you import any modules you wish | ||
to be type checked. Give it the name of your top level package (or a list of package names):: | ||
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from typeguard.importhook import install_import_hook | ||
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install_import_hook('myapp') | ||
from myapp import some_module # import only AFTER installing the hook, or it won't take effect | ||
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If you wish, you can uninstall the import hook:: | ||
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manager = install_import_hook('myapp') | ||
from myapp import some_module | ||
manager.uninstall() | ||
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or using the context manager approach:: | ||
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with install_import_hook('myapp'): | ||
from myapp import some_module | ||
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You can also customize the logic used to select which modules to instrument:: | ||
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from typeguard.importhook import TypeguardFinder, install_import_hook | ||
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class CustomFinder(TypeguardFinder): | ||
def should_instrument(self, module_name: str): | ||
# disregard the module names list and instrument all loaded modules | ||
return True | ||
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install_import_hook('', cls=CustomFinder) | ||
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Using the pytest plugin | ||
----------------------- | ||
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Typeguard comes with a pytest plugin that installs the import hook (explained in the previous | ||
section). To use it, run ``pytest`` with the appropriate ``--typeguard-packages`` option. For | ||
example, if you wanted to instrument the ``foo.bar`` and ``xyz`` packages for type checking, you | ||
can do the following: | ||
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.. code-block:: bash | ||
pytest --typeguard-packages=foo.bar,xyz | ||
There is currently no support for specifying a customized module finder. | ||
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Checking types directly | ||
----------------------- | ||
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Typeguard can also be used as a beefed-up version of :func:`isinstance` that also supports checking | ||
against annotations in the :mod:`typing` module:: | ||
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from typeguard import check_type | ||
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# Raises TypeError if there's a problem | ||
check_type('variablename', [1234], List[int]) | ||
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Supported typing.* types | ||
------------------------ | ||
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The following types from the ``typing`` package have specialized support: | ||
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=============== ============================================================= | ||
Type Notes | ||
=============== ============================================================= | ||
``AbstractSet`` Contents are typechecked | ||
``Callable`` Argument count is checked but types are not (yet) | ||
``Dict`` Keys and values are typechecked | ||
``List`` Contents are typechecked | ||
``Literal`` | ||
``NamedTuple`` Field values are typechecked | ||
``Protocol`` Value type checked with ``issubclass()`` against the protocol | ||
``Set`` Contents are typechecked | ||
``Sequence`` Contents are typechecked | ||
``Tuple`` Contents are typechecked | ||
``Type`` | ||
``TypedDict`` Contents are typechecked | ||
``TypeVar`` Constraints, bound types and co/contravariance are supported | ||
but custom generic types are not (due to type erasure) | ||
``Union`` | ||
=============== ============================================================= |
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