PyCharm 2018.2 Help

Type Hinting in PyCharm

PyCharm provides various means to assist inspecting and checking the types of the objects in your script. PyCharm supports type hinting in function annotations and type comments using the typing module and the format defined by PEP 484.

Adding type hints

Although PyCharm supports all methods for adding types supported in PEP 484, using type hints through intention actions is the most convenient way. Depending on the interpreter you use, the type is added as an annotation (Python 3) or as a comment (Python 2).

To add a type hint, follow these steps:

  1. Select a code element.
  2. Press Alt+Enter.
  3. Select Add type hint for ....
  4. Press Enter to complete the action or edit the type if appropriate.
ExampleIntention ActionResulting Code for comments (Python 2)Resulting Code for annotations (Python 3)
example of adding a type hint for a variable
example of adding a type hint for a variable (Python 2)
example of adding a type hint for a variable (Python 3)
example of adding a type hint for a function
example of adding a type hint for a function (Python 2)
example of adding a type hint for a function (Python 3)
Class attributes
example of adding a type hint for a class attribute
example of adding a type hint for a class attribute (Python 2)
example of adding a type hint for a class attribute (Python 3)

You can also use Python stubs or comments to specify the types of variables, functions, and class fields.

Specifying types by using comments

Use a # type: comment to specify the types of local variables and attributes:

py type hinting attributes

Converting comments

For comment-based type hints, PyCharm suggests an intention action that allows you to convert comment-based type hint to a variable annotation. This intention has the name Convert to variable annotation, and works as follows:

from typing import List, Optional xs = [] # type: List[Optional[str]]
from typing import List, Optional xs: List[Optional[str]] = []

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:

py stub1

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

py stub2

Using Typeshed

Typeshed is a set of files with type annotations for the standard Python library and various packages. Typeshed stubs provide definitions for Python classes, functions, and modules defined with type hints. PyCharm uses this information for better code completion, inspections, and other code insight features.

PyCharm is switching to Typeshed, the common repository for Python stubs. The Typeshed stubs bundled with PyCharm are shown in the project view under the node External Libraries | <Python interpreter> | Typeshed Stubs. Note that PyCharm currently uses only a few of the bundled stubs (i.e. builtins.pyi, typing.pyi, and several others).

To override the bundled Typeshed repository with your own version, follow these steps:

  1. Copy some or all the stubs into a directory in your project.
  2. Mark a directory as a source root by choosing Mark Directory as | Sources Root from the context menu of the directory.

The Python skeletons repository is now deprecated.

Type hints validation

Any time you're applying type hints, PyCharm checks if the type is used correctly. If there is a usage error, the corresponding warning is shown and the recommended action is suggested. Below are the validation examples.

Validation errorSuggested action
Duplication of type declaration.
incorrect type hint
Remove either of the type declarations.
Number of arguments in the type declaration differs from the number of function arguments.
too many arguments
Adjust the number of the arguments.
Missing brackets.
missing bracket
Add the required brackets where appropriate.

Type comments with unpacking do not match the corresponding targets.

incorrect type for unpacked variables

Check the target format and modify the type comment accordingly.

Incorrect syntax of Callable parameters.
Incorrect Callable format
Use the suggested format and add the required brackets to wrap Callable parameters.
Last modified: 14 July 2018

See Also