unkey

A tool and pre-commit hook to automatically remove extra calls to keys().

Installation

pip install unkey

As a pre-commit hook

See pre-commit for instructions

Sample .pre-commit-config.yaml:

-   repo: https://github.com/mxr/unkey
    rev: v0.0.2
    hooks:
    -   id: unkey

Overview

Summary

Iterating over a Python dictionary will iterate over its keys, so calls to keys() are often not needed. Removing these calls keeps your code terser and more readable.

Excluding Code

unkey does not support an equivalent of flake8's # noqa or mypy's #type: ignore to stop rewriting. Until this feature is available, use an intermediate variable to prevent rewriting.

# will be rewritten
min({1: 2, 3: 4}.keys())  # becomes min({1: 2, 3: 4})

# will not be rewritten
keys = {1: 2, 3: 4}.keys()
min(keys)

Disclaimer

Since AST parsing does not always tell us the type of an object, there may be false positives and undesirable rewrites or bugs. With that said the tool is designed to err on the side of not rewriting rather than being very clever and rewriting as much as possible. To exclude rewrite, see the above section. PRs are always welcome to help out!

Features

builtins

Rewrites builtin calls that have iterable arguments

 # simple cases
-min({1: 2, 3: 4}.keys())
+min({1: 2, 3: 4})

-min(d.keys())
+min(d)

-min(f().keys())
+min(f())

 # more complex cases
-min(d1().x.y(1, 2 ,3, (4, 5)).keys())
+min(d1().x.y(1, 2, 3, (4, 5)))

zip

Rewrites relevant arguments in zip()

-zip(d.keys(), {}.keys(), f().keys(), [1, 2, 3])
+zip(d, {}, f(), [1, 2, 3])

map / filter

Rewrites relevant arguments in map and filter

-map(lambda x: x*2, d.keys())
+map(lambda x: x*2, d)

-filter(None, d.keys())
+filteR(None, d)

in

Rewrites relevant comparisons using in

-if x in d.keys():
+if x in d:
     pass

comprehensions

Rewrites relevant list/dict/set comprehensions and generator expressions

-[x for x in d.keys()]
+[x for x in d]

-(x for x in d.keys())
+(x for x in d)

-{x for x in d.keys()}
+{x for x in d}

-{x: x for x in d.keys()}
+{x: x for x in d}

For additional linting in this space check out flake8-comprehensions.

iteration

Rewrites iteration

-for _ in d.keys(): pass
+for _ in d: pass

-for _ in {}.keys(): pass
+for _ in {}: pass

-for _ in f().keys(): pass
+for _ in f(): pass

Acknowledgements

This tool would not be possible without guidance and tools from Anthony Sottile, specifically, pyupgrade and pre-commit. unkey is heavily adapted from the former and code is attributed wherever possible. Thank you!