Type Hinting in PyCharm

In this section:

• Following PEP484
  • Specifying types of parameters
  • Specifying return types
  • Specifying types of local variables and attributes
  • Python stubs
• Legacy type syntax for docstrings
  • Specifying types of local variables
  • Specifying types of fields
  • Specifying return types
  • Specifying parameter types

Following PEP484

PyCharm supports type hinting in function annotations and type comments using the typing module defined by PEP 484.

Specifying types of parameters

When Python 3 is specified as the project interpreter, you can use annotations to specify the expected parameter type:

For Python 2, you can specify the types of parameters in the Python stubs.

Specifying return types

When Python 3 is specified as the project interpreter, you can use annotations to specify the expected return type:

For Python 2, you can specify return types in the Python stubs.

Specifying types of local variables and attributes

Use annotations to specify the types of local variables and attributes:

Also, you can specify the types of local variables and attributes in the Python stubs.

Python stubs

PyCharm supports Python stub files with the .pyi extension. These files allow you to specify the type hints using Python 3 syntax for both Python 2 and 3.

The stub files are created as usual , but you must specify the extension .pyi explicitly.

PyCharm shows an asterisk in the left gutter for those Python files that have stubs:

Clicking the asterisk results in jumping to the corresponding file with the .pyi extension:

Legacy type syntax for docstrings

PyCharm supports legacy approach to specifying types in Python using docstrings. So doing, the supported formats are:

• reStructuredText
• epytext
• NumPy
• Google

To choose the desired docstring format, use the Python Intergated Tools page of the Settings/Preferences dialog.

Type syntax in Python docstrings is not defined by any standard. Thus, PyCharm suggests the following notation:

Specifying types of local variables

Consider adding information about the expected type of a local variable using :type or @type docstrings:

It is also possible to use isinstance to define the expected local variable type:

Specifying types of fields

You can use type hinting to specify the expected type of fields:

Alternatively, you can specify types of fields in the docstring of a class:

Specifying return types

Use docstrings :rtype or @rtype to specify the expected return type:

• :rtype: collections.Iterable[int] # return type: 'items' is of type generator or collections.Iterable, 'a' is of type int, see the following code:
  def my_iter(): for i in range(10): yield i items = my_iter() for a in items: print a
• :rtype: list[int] for my_iter # return type: 'a' is of type int, see the following code:
  def my_iter(): for i in range(10): yield i for a in my_iter(): print a

Specifying parameter types

Consider adding information about the expected parameter type. This information is specified using :type or @type docstrings, for example, :param "type_name" "param_name": "param_description".