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Typed lambdas that are short and readable

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Build Status Coverage Status Documentation Status Python Version wemake-python-styleguide Checked with mypy

Write short and fully-typed lambdas where you need them.


  • Allows to write lambdas as _
  • Fully typed with annotations and checked with mypy, PEP561 compatible
  • Has a bunch of helpers for better composition
  • Easy to start: has lots of docs, tests, and tutorials


pip install lambdas

We also recommend to use the same mypy settings we use.


Imagine that you need to sort an array of dictionaries like so:

scores = [
    {'name': 'Nikita', 'score': 2},
    {'name': 'Oleg', 'score': 1},
    {'name': 'Pavel', 'score': 4},

print(sorted(scores, key=lambda item: item['score']))

And it works perfectly fine. Except, that you have to do a lot of typing for such a simple operation.

That's where lambdas helper steps in:

scores = [
    {'name': 'Nikita', 'score': 2},
    {'name': 'Oleg', 'score': 1},
    {'name': 'Pavel', 'score': 4},

print(sorted(scores, key=_['score']))

It might really save you a lot of effort, when you use a lot of lambda functions. Like when using returns library.

Work in progress:

  • _.some_attribute is not supported yet, because we need a complex mypy plugin for this
  • _.method() is not supported yet for the same reason
  • TypedDicts are not tested with __getitem__
  • __getitem__ does not work with list and tuples (collections), only dicts (mappings)

For now you will have to use regular lamdbas in these cases.

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