MonkeyType collects runtime types of function arguments and return values, and can automatically generate stub files or even add draft type annotations directly to your Python code based on the types collected at runtime.


Run a script under call-trace logging of functions and methods in all imported modules:

$ monkeytype run

Or enable call-trace logging for a block of code:

import monkeytype

with monkeytype.trace():

By default this will dump call traces into a sqlite database in the file monkeytype.sqlite3 in the current working directory. You can then use the monkeytype command to generate a stub file for a module, or apply the type annotations directly to your code:

$ monkeytype stub some.module
$ monkeytype apply some.module


MonkeyType requires Python 3.6+ and the retype library (for applying type stubs to code files). It generates only Python 3 type annotations (no type comments).


Install MonkeyType with pip:

pip install MonkeyType

How MonkeyType works

MonkeyType uses the sys.setprofile hook provided by Python to interpose on function calls, function returns, and generator yields, and record the types of arguments / return values / yield values.

It generates stub files based on that data, and can use retype to apply those stub files directly to your code.

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