Statically check and infer types for unannotated Python code.
Pytype is a static analyzer that helps you find type errors in Python code. It can type-check code with or without type annotations, as well as generate annotations. Pytype runs under Python 2.7 or 3.5+ and analyzes both Python 2 and Python 3 code.
$ cat foo.py def make_greeting(user_id): return 'hello, user' + user_id def print_greeting(): print(make_greeting(0))
Run pytype to catch the bug:
$ pytype foo.py File "foo.py", line 2, in make_greeting: unsupported operand type(s) for +: 'str' and 'int' [unsupported-operands] str.__add__ expected str Traceback: line 5, in print_greeting
Merge pytype's generated type information back into
$ cat pytype_output/foo.pyi def make_greeting(user_id) -> str: ... def print_greeting() -> None: ... $ merge-pyi -i foo.py pytype_output/foo.pyi $ cat foo.py def make_greeting(user_id) -> str: return 'hello, user' + user_id def print_greeting() -> None: print(make_greeting(0))
You need a Python 2.7 or 3.5+ interpreter to run pytype, as well as an
$PATH for the Python version of the code you're analyzing.
- Pytype is currently developed and tested on Linux, which is the main supported platform.
- Installation on MacOSX requires OSX 10.7 or higher and Xcode v8 or higher.
- Windows is currently not supported.
The rest of this document provides complete instructions for installing and using pytype. To quickly get started with some common workflows, check out the following docs:
Pytype can be installed via pip. Note that the installation requires
setuptools. (If you're working in a virtualenv, these two packages should
already be present.)
pip install pytype
Or from the source code on GitHub.
git clone --recurse-submodules https://github.com/google/pytype.git cd pytype pip install -U .
Instead of using
--recurse-submodules, you could also have run
git submodule init git submodule update
usage: pytype [options] input [input ...] positional arguments: input file or directory to process
-V, --python-version: Python version (major.minor) of the target code. Defaults to
-o, --output: The directory into which all pytype output goes, including generated .pyi files. Defaults to
-P, --pythonpath. Paths to source code directories, separated by ':'. Defaults to an educated guess based on
-d, --disable. Comma separated list of error names to ignore. Detailed explanations of pytype's error names are in this doc. Defaults to empty.
For a full list of options, run
In addition to the above, you can direct pytype to use a custom typeshed
installation instead of its own bundled copy by setting
For convenience, you can save your pytype configuration in a file. The config
file is an INI-style file with a
[pytype] section; if an explicit config file
is not supplied, pytype will look for a
[pytype] section in the first
setup.cfg file found by walking upwards from the current working directory.
Start off by generating a sample config file:
$ pytype --generate-config pytype.cfg
Now customize the file based on your local setup, keeping only the sections you need. Directories may be relative to the location of the config file, which is useful if you want to check in the config file as part of your project.
For example, suppose you have the following directory structure and want to
~/repo1/foo, which depends on package
~/ ├── repo1 │ └── foo │ ├── __init__.py │ └── file_to_check.py └── repo2 └── bar ├── __init__.py └── dependency.py
Here is the filled-in config file, which instructs pytype to type-check
~/repo1/foo as Python 3.6 code, look for packages in
and ignore attribute errors. Notice that the path to a package does not include
the package itself.
$ cat ~/repo1/pytype.cfg # NOTE: All relative paths are relative to the location of this file. [pytype] # Space-separated list of files or directories to process. inputs = foo # Python version (major.minor) of the target code. python_version = 3.6 # Paths to source code directories, separated by ':'. pythonpath = .: ~/repo2 # Comma separated list of error names to ignore. disable = attribute-error
We could've discovered that
~/repo2 needed to be added to the pythonpath by
running pytype's broken dependency checker:
$ pytype --config=~/repo1/pytype.cfg ~/repo1/foo/*.py --unresolved Unresolved dependencies: bar.dependency
Pytype ships with three scripts in addition to
merge-pyi, for merging type information from a .pyi file into a Python file.
pytd, a parser for .pyi files.
pytype-single, a debugging tool for pytype developers, which analyzes a single Python file assuming that .pyi files have already been generated for all of its dependencies.
- Windows support
- A rerun mode to only reanalyze files that have changed since the last run
This is not an official Google product.