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Auto-generate PEP-484 annotations

Project README

PyAnnotate: Auto-generate PEP-484 annotations

Insert annotations into your source code based on call arguments and return types observed at runtime.

For license and copyright see the end of this file.

Blog post:

How to use

See also the example directory.

Phase 1: Collecting types at runtime

  • Install the usual way (see "red tape" section below)
  • Add from pyannotate_runtime import collect_types to your test
  • Early in your test setup, call collect_types.init_types_collection()
  • Bracket your test execution between calls to collect_types.start() and collect_types.stop() (or use the context manager below)
  • When done, call collect_types.dump_stats(filename)

All calls between the start() and stop() calls will be analyzed and the observed types will be written (in JSON form) to the filename you pass to dump_stats(). You can have multiple start/stop pairs per dump call.

If you'd like to automatically collect types when you run pytest, see example/ and example/

Instead of using start() and stop() you can also use a context manager:

with collect_types.collect():
    <your code here>

Phase 2: Inserting types into your source code

The command-line tool pyannotate can add annotations into your source code based on the annotations collected in phase 1. The key arguments are:

  • Use --type-info FILE to tell it the file you passed to dump_stats()
  • Positional arguments are source files you want to annotate
  • With no other flags the tool will print a diff indicating what it proposes to do but won't do anything. Review the output.
  • Add -w to make the tool actually update your files. (Use git or some other way to keep a backup.)

At this point you should probably run mypy and iterate. You probably will have to tweak the changes to make mypy completely happy.

Notes and tips

  • It's best to do one file at a time, at least until you're comfortable with the tool.
  • The tool doesn't touch functions that already have an annotation.
  • The tool can generate either of:
    • type comments, i.e. Python 2 style annotations
    • inline type annotations, i.e. Python 3 style annotations, using --py3 in v1.0.7+

Red tape


This should work for Python 2.7 as well as for Python 3.4 and higher.

pip install pyannotate

This installs several items:

  • A runtime module, pyannotate_runtime/, which collects and dumps types observed at runtime using a profiling hook.

  • A library package, pyannotate_tools, containing code that can read the data dumped by the runtime module and insert annotations into your source code.

  • An entry point, pyannotate, which runs the library package on your files.

For dependencies, see and requirements.txt.

Testing etc.

To run the unit tests, use pytest:



We'd love your help with some of these issues:

  • Better documentation.
  • Python 3 code generation.
  • Refactor the tool modules (currently its legacy architecture shines through).


The following people contributed significantly to this tool:

  • Tony Grue
  • Sergei Vorobev
  • Jukka Lehtosalo
  • Guido van Rossum

Licence etc.

  1. License: Apache 2.0.
  2. Copyright attribution: Copyright (c) 2017 Dropbox, Inc.
  3. External contributions to the project should be subject to Dropbox's Contributor License Agreement (CLA):
Open Source Agenda is not affiliated with "Pyannotate" Project. README Source: dropbox/pyannotate
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