❄️ A flake8 plugin to help you write better list/set/dict comprehensions.

Overview

flake8-comprehensions

https://img.shields.io/github/workflow/status/adamchainz/flake8-comprehensions/CI/main?style=for-the-badge https://img.shields.io/pypi/v/flake8-comprehensions.svg?style=for-the-badge https://img.shields.io/badge/code%20style-black-000000.svg?style=for-the-badge pre-commit

A flake8 plugin that helps you write better list/set/dict comprehensions.

Requirements

Python 3.6 to 3.9 supported.

Installation

First, install with pip:

python -m pip install flake8-comprehensions

Second, check that flake8 lists the plugin in its version line:

$ flake8 --version
3.7.8 (flake8-comprehensions: 3.0.0, mccabe: 0.6.1, pycodestyle: 2.5.0, pyflakes: 2.1.1) CPython 3.8.0 on Linux

Third, add the C4 prefix to your select list. For example, if you have your configuration in setup.cfg:

[flake8]
select = E,F,W,C4

Linting a Django project? Check out my book Speed Up Your Django Tests which covers loads of best practices so you can write faster, more accurate tests.


Rules

C400-402: Unnecessary generator - rewrite as a <list/set/dict> comprehension.

It's unnecessary to use list, set, or dict around a generator expression, since there are equivalent comprehensions for these types. For example:

  • Rewrite list(f(x) for x in foo) as [f(x) for x in foo]
  • Rewrite set(f(x) for x in foo) as {f(x) for x in foo}
  • Rewrite dict((x, f(x)) for x in foo) as {x: f(x) for x in foo}

C403-404: Unnecessary list comprehension - rewrite as a <set/dict> comprehension.

It's unnecessary to use a list comprehension inside a call to set or dict, since there are equivalent comprehensions for these types. For example:

  • Rewrite set([f(x) for x in foo]) as {f(x) for x in foo}
  • Rewrite dict([(x, f(x)) for x in foo]) as {x: f(x) for x in foo}

C405-406: Unnecessary <list/tuple> literal - rewrite as a <set/dict> literal.

It's unnecessary to use a list or tuple literal within a call to set or dict. For example:

  • Rewrite set([1, 2]) as {1, 2}
  • Rewrite set((1, 2)) as {1, 2}
  • Rewrite set([]) as set()
  • Rewrite dict([(1, 2)]) as {1: 2}
  • Rewrite dict(((1, 2),)) as {1: 2}
  • Rewrite dict([]) as {}

C407: Unnecessary <dict/list> comprehension - <builtin> can take a generator

It's unnecessary to pass a list comprehension to some builtins that can take generators instead. For example:

  • Rewrite sum([x ** 2 for x in range(10)]) as sum(x ** 2 for x in range(10))
  • Rewrite all([foo.bar for foo in foos]) as all(foo.bar for foo in foos)
  • Rewrite filter(lambda x: x % 2 == 0, [x ** 3 for x in range(10)]) as filter(lambda x: x % 2 == 0, (x ** 3 for x in range(10)))

The list of builtins that are checked for are:

  • all
  • any
  • enumerate
  • filter
  • frozenset
  • map
  • max
  • min
  • sorted
  • sum
  • tuple

C408: Unnecessary <dict/list/tuple> call - rewrite as a literal.

It's slower to call e.g. dict() than using the empty literal, because the name dict must be looked up in the global scope in case it has been rebound. Same for the other two basic types here. For example:

  • Rewrite dict() as {}
  • Rewrite dict(a=1, b=2) as {"a": 1, "b": 2}
  • Rewrite list() as []
  • Rewrite tuple() as ()

C409-410: Unnecessary <list/tuple> passed to <list/tuple>() - (remove the outer call to <list/tuple>``()/rewrite as a ``<list/tuple> literal).

It's unnecessary to use a list or tuple literal within a call to list or tuple, since there is literal syntax for these types. For example:

  • Rewrite tuple([1, 2]) as (1, 2)
  • Rewrite tuple((1, 2)) as (1, 2)
  • Rewrite tuple([]) as ()
  • Rewrite list([1, 2]) as [1, 2]
  • Rewrite list((1, 2)) as [1, 2]
  • Rewrite list([]) as []

C411: Unnecessary list call - remove the outer call to list().

It's unnecessary to use a list around a list comprehension, since it is equivalent without it. For example:

  • Rewrite list([f(x) for x in foo]) as [f(x) for x in foo]

C412: Unnecessary <dict/list/set> comprehension - 'in' can take a generator.

It's unnecessary to pass a dict/list/set comprehension to 'in', as it can take a generator instead. For example:

  • Rewrite y in [f(x) for x in foo] as y in (f(x) for x in foo)
  • Rewrite y in {x ** 2 for x in foo} as y in (x ** 2 for x in foo)

C413: Unnecessary <list/reversed> call around sorted().

It's unnecessary to use list() around sorted() as it already returns a list. It is also unnecessary to use reversed() around sorted() as the latter has a reverse argument. For example:

  • Rewrite list(sorted([2, 3, 1])) as sorted([2, 3, 1])
  • Rewrite reversed(sorted([2, 3, 1])) as sorted([2, 3, 1], reverse=True)
  • Rewrite reversed(sorted([2, 3, 1], reverse=True)) as sorted([2, 3, 1])

C414: Unnecessary <list/reversed/set/sorted/tuple> call within <list/set/sorted/tuple>().

It's unnecessary to double-cast or double-process iterables by wrapping the listed functions within list/set/sorted/tuple. For example:

  • Rewrite list(list(iterable)) as list(iterable)
  • Rewrite list(tuple(iterable)) as list(iterable)
  • Rewrite tuple(list(iterable)) as tuple(iterable)
  • Rewrite tuple(tuple(iterable)) as tuple(iterable)
  • Rewrite set(set(iterable)) as set(iterable)
  • Rewrite set(list(iterable)) as set(iterable)
  • Rewrite set(tuple(iterable)) as set(iterable)
  • Rewrite set(sorted(iterable)) as set(iterable)
  • Rewrite set(reversed(iterable)) as set(iterable)
  • Rewrite sorted(list(iterable)) as sorted(iterable)
  • Rewrite sorted(tuple(iterable)) as sorted(iterable)
  • Rewrite sorted(sorted(iterable)) as sorted(iterable)
  • Rewrite sorted(reversed(iterable)) as sorted(iterable)

C415: Unnecessary subscript reversal of iterable within <reversed/set/sorted>().

It's unnecessary to reverse the order of an iterable when passing it into one of the listed functions will change the order again. For example:

  • Rewrite set(iterable[::-1]) as set(iterable)
  • Rewrite sorted(iterable[::-1]) as sorted(iterable, reverse=True)
  • Rewrite reversed(iterable[::-1]) as iterable

C416: Unnecessary <list/set> comprehension - rewrite using <list/set>().

It's unnecessary to use a list comprehension if the elements are unchanged. The iterable should be wrapped in list() or set() instead. For example:

  • Rewrite [x for x in iterable] as list(iterable)
  • Rewrite {x for x in iterable} as set(iterable)
Owner
Adam Johnson
🦄 @django technical board member 🇬🇧 @djangolondon co-organizer ✍ AWS/Django/Python Author and Consultant
Adam Johnson
Mylint - My really simple rendition of how a linter works.

mylint My really simple rendition of how a linter works. This original version was written for my AST article. Since then I've added tests and turned

Tushar Sadhwani 2 Dec 29, 2021
Flake8 extension for checking quotes in python

Flake8 Extension to lint for quotes. Major update in 2.0.0 We automatically encourage avoiding escaping quotes as per PEP 8. To disable this, use --no

Zachary Heller 157 Dec 13, 2022
Pymxs, the 3DsMax bindings of Maxscript to Python doesn't come with any stubs

PyMXS Stubs generator What Pymxs, the 3DsMax bindings of Maxscript to Python doe

Frieder Erdmann 19 Dec 27, 2022
Easy saving and switching between multiple KDE configurations.

Konfsave Konfsave is a config manager. That is, it allows you to save, back up, and easily switch between different (per-user) system configurations.

42 Sep 25, 2022
A simple program which checks Python source files for errors

Pyflakes A simple program which checks Python source files for errors. Pyflakes analyzes programs and detects various errors. It works by parsing the

Python Code Quality Authority 1.2k Dec 30, 2022
Rust like Option and Result types in Python

Option Rust-like Option and Result types in Python, slotted and fully typed. An Option type represents an optional value, every Option is either Some

45 Dec 13, 2022
Unbearably fast O(1) runtime type-checking in pure Python.

Look for the bare necessities, the simple bare necessities. Forget about your worries and your strife. — The Jungle Book.

beartype 1.4k Jan 01, 2023
The official GitHub mirror of https://gitlab.com/pycqa/flake8

Flake8 Flake8 is a wrapper around these tools: PyFlakes pycodestyle Ned Batchelder's McCabe script Flake8 runs all the tools by launching the single f

Python Code Quality Authority 2.6k Jan 03, 2023
A Pylint plugin to analyze Flask applications.

pylint-flask About pylint-flask is Pylint plugin for improving code analysis when editing code using Flask. Inspired by pylint-django. Problems pylint

Joe Schafer 62 Sep 18, 2022
flake8 plugin to run black for checking Python coding style

flake8-black Introduction This is an MIT licensed flake8 plugin for validating Python code style with the command line code formatting tool black. It

Peter Cock 146 Dec 15, 2022
Backport Python 3.8+ typing utils & add issubtype & more

typing-utils Backport Python3.8+ typing utils & issubtype & more Install API issubtype get_origin get_args get_type_hints Install pip install typi

10 Nov 09, 2022
Stubs with type annotations for ordered-set Python library

ordered-set-stubs - stubs with type annotations for ordered-set Python library Archived - now type annotations are the part of the ordered-set library

Roman Inflianskas 2 Feb 06, 2020
Enforce the same configuration across multiple projects

Nitpick Flake8 plugin to enforce the same tool configuration (flake8, isort, mypy, Pylint...) across multiple Python projects. Useful if you maintain

Augusto W. Andreoli 315 Dec 25, 2022
Static type checker for Python

Static type checker for Python Speed Pyright is a fast type checker meant for large Python source bases. It can run in a “watch” mode and performs fas

Microsoft 9.2k Jan 03, 2023
Mypy stubs, i.e., type information, for numpy, pandas and matplotlib

Mypy type stubs for NumPy, pandas, and Matplotlib This is a PEP-561-compliant stub-only package which provides type information for matplotlib, numpy

Predictive Analytics Lab 194 Dec 19, 2022
flake8 plugin to catch useless `assert` statements

flake8-useless-assert flake8 plugin to catch useless assert statements Download or install on the PyPI page Violations Code Description Example ULA001

1 Feb 12, 2022
A plugin for flake8 integrating Mypy.

flake8-mypy NOTE: THIS PROJECT IS DEAD It was created in early 2017 when Mypy performance was often insufficient for in-editor linting. The Flake8 plu

Łukasz Langa 103 Jun 23, 2022
Mypy plugin and stubs for SQLAlchemy

Pythonista Stubs Stubs for the Pythonista iOS API. This allows for better error detection and IDE / editor autocomplete. Installation and Usage pip in

Dropbox 521 Dec 29, 2022
:sparkles: Surface lint errors during code review

✨ Linty Fresh ✨ Keep your codebase sparkly clean with the power of LINT! Linty Fresh parses lint errors and report them back to GitHub as comments on

Lyft 183 Dec 18, 2022
The mypy playground. Try mypy with your web browser.

mypy-playground The mypy playground provides Web UI to run mypy in the sandbox: Features Web UI and sandbox for running mypy eas

Yusuke Miyazaki 57 Jan 02, 2023