What's the correct way to sort Python `import x` and `from x import y` statements?

问题

The python style guide suggests to group imports like this:

Imports should be grouped in the following order:

1. standard library imports
2. related third party imports
3. local application/library specific imports

However, it does not mention anything how the two different ways of imports should be laid out:

from foo import bar
import foo

There are multiple ways to sort them (let's assume all those import belong to the same group):

• first from..import, then import

  from g import gg
  from x import xx
  import abc
  import def
  import x
  

• first import, then from..import

  import abc
  import def
  import x
  from g import gg
  from x import xx
  

• alphabetic order by module name, ignoring the kind of import

  import abc
  import def
  from g import gg
  import x
  from xx import xx
  

PEP8 does not mention the preferred order for this and the "cleanup imports" features some IDEs have probably just do whatever the developer of that feature preferred.

I'm looking for another PEP clarifying this or a relevant comment/email from the BDFL (or another Python core developer). Please don't post subjective answers stating your own preference.

回答1:

Imports are generally sorted alphabetically and described in various places beside PEP 8.

Alphabetically sorted modules are quicker to read and searchable. After all python is all about readability. Also It is easier to verify that something is imported, and avoids duplicated imports

There is nothing available in PEP 8 regarding sorting.So its all about choice what you use.

According to few references from reputable sites and repositories also popularity, Alphabetical ordering is the way.

for eg like this:

import httplib
import logging
import random
import StringIO
import time
import unittest
from nova.api import openstack
from nova.auth import users
from nova.endpoint import cloud

OR

import a_standard
import b_standard

import a_third_party
import b_third_party

from a_soc import f
from a_soc import g
from b_soc import d

Reddit official repository also states that, In general PEP-8 import ordering should be used. However there are a few additions which is

for each imported group the order of imports should be:
import <package>.<module> style lines in alphabetical order
from <package>.<module> import <symbol> style in alphabetical order

References:

• https://code.google.com/p/soc/wiki/PythonStyleGuide
• https://github.com/reddit/reddit/wiki/PythonImportGuidelines
• http://docs.openstack.org/developer/hacking/
• http://developer.plone.org/reference_manuals/external/plone.api/contribute/conventions.html#grouping-and-sorting

PS: the isort utility automatically sorts your imports.

回答2:

According to the CIA's internal coding conventions (part of the WikiLeaks Vault 7 leak), python imports should be grouped into three groups:

1. Standard library imports
2. Third-party imports
3. Application-specific imports

Imports should be ordered lexicographically within these groups, ignoring case:

import foo
from foo import bar
from foo.bar import baz
from foo.bar import Quux
from Foob import ar

回答3:

The PEP 8 says nothing about it indeed. There's no convention for this point, and it doesn't mean the Python community need to define one absolutely. A choice can be better for a project but the worst for another... It's a question of preferences for this, since each solutions has pro and cons. But if you want to follow conventions, you have to respect the principal order you quoted:

1. standard library imports
2. related third party imports
3. local application/library specific imports

For example, Google recommend in this page that import should be sorted lexicographically, in each categories (standard/third parties/yours). But at Facebook, Yahoo and whatever, it's maybe another convention...

回答4:

I highly recommend reorder-python-imports. It follows the 2nd option of the accepted answer and also integrates into pre-commit, which is super helpful.

回答5:

All import x statements should be sorted by the value of x and all from x import y statements should be sorted by the value of x in alphabetical order and the sorted groups of from x import y statements must follow the sorted group of import x statements.

import abc
import def
import x
from g import gg
from x import xx
from z import a

来源：https://stackoverflow.com/questions/20762662/whats-the-correct-way-to-sort-python-import-x-and-from-x-import-y-statement