Type Hinting in PyCharm

In this section:

• Basics
• Type syntax
• Specifying types of parameters
• Specifying return types
• Specifying types of local variables
• Specifying types of fields

Basics

Python is dynamically typed. That's why one doesn't need to specify variable types explicitly. However, it is possible to use docstrings (reStructuredText, epytext) and py3 annotations to specify information about the expected types of the following values:

• parameters passed to a function
• return values
• local variables
• fields

PyCharm suggests code completion with these expected types.

Type syntax

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

Syntax	Description
Foo	Class Foo visible in the current scope
x.y.Bar	Class Bar from x.y module
Foo | Bar	Foo or Bar
(Foo, Bar)	Tuple of Foo and Bar
list[Foo]	List of Foo elements
dict[Foo, Bar]	Dict from Foo to Bar
T	Generic type (T-Z are reserved for generics)
T <= Foo	Generic type with upper bound Foo
Foo[T]	Foo parameterized with T
(Foo, Bar) -> Baz	Function of Foo and Bar that returns Baz
list[dict[str, datetime]]	List of dicts from str to datetime (nested arguments)

Specifying types of parameters

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".

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

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
              

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

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

Finally, you can use type hinting to specify the expected type of fields: