zimports 0.3.0

zzzeek why are you writing one of these, there are a dozen pep8 import fixers

I’ve just gone through a whole bunch. I need one that:

• works directly with flake8-import-order so we are guaranteed to have a match

• has shell capability, not only a plugin for vim or sublime text (Python Fix Imports, gratis)

• Removes unused imports, not just reformats them (importanize)

• Reformats imports, not just removes unused ones (autoflake)

• Doesn’t miss removing an import that isn’t used just because it’s on a multiline import (autoflake)

• Breaks up all imports into individual lines, not just if the line is >80 char (importanize)

• Is still pretty simple (we’re a bit beyond our original “extremely” simple baseline, because all problems are ultimately not that simple) because (since pyflakes and now flake8-import-order do most of the hard work) this is an extremely simple job, there’s (still) no need for a giant application here.

Usage

The script can run without any configuration, options are as follows:

$ zimports --help
usage: zimports [-h] [-m APPLICATION_IMPORT_NAMES]
                [-p APPLICATION_PACKAGE_NAMES] [--style STYLE] [-k]
                [--heuristic-unused HEURISTIC_UNUSED] [--statsonly] [-e]
                [--diff] [--stdout]
                filename [filename ...]

positional arguments:
  filename              Python filename(s) or directories

optional arguments:
  -h, --help            show this help message and exit
  -m APPLICATION_IMPORT_NAMES, --application-import-names APPLICATION_IMPORT_NAMES
                        comma separated list of names that should be
                        considered local to the application. reads from
                        [flake8] application-import-names by default.
  -p APPLICATION_PACKAGE_NAMES, --application-package-names APPLICATION_PACKAGE_NAMES
                        comma separated list of names that should be
                        considered local to the organization. reads from
                        [flake8] application-package-names by default.
  --style STYLE         import order styling, reads from [flake8] import-
                        order-style by default, or defaults to 'google'
  --multi-imports       If set, multiple imports can exist on one line
  -k, --keep-unused     keep unused imports even though detected as unused
  --heuristic-unused HEURISTIC_UNUSED
                        Remove unused imports only if number of imports is
                        less than <HEURISTIC_UNUSED> percent of the total
                        lines of code
  --statsonly           don't write or display anything except the file stats
  -e, --expand-stars    Expand star imports into the names in the actual
                        module, which can then have unused names removed.
                        Requires modules can be imported
  --diff                don't modify files, just dump out diffs
  --stdout              dump file output to stdout

Typically, configuration will be in setup.cfg for flake8 (support for tox.ini, pyproject.toml is TODO):

[flake8]
enable-extensions = G
ignore =
    A003,
    E203,E305,E711,E712,E721,E722,E741,
    F841,
    N801,N802,N806,
    W503,W504
import-order-style = google
application-import-names = sqlalchemy,test

Then, a typical run on a mostly clean source tree looks like:

$ zimports lib/
[Unchanged]     lib/sqlalchemy/inspection.py (in 0.0058 sec)
[Unchanged]     lib/sqlalchemy/log.py (in 0.0221 sec)

...

[Unchanged]     lib/sqlalchemy/orm/attributes.py (in 0.2152 sec)
[Unchanged]     lib/sqlalchemy/orm/base.py (in 0.0363 sec)
[Writing]       lib/sqlalchemy/orm/relationships.py ([2% of lines are imports] [source +0L/-2L] [3 imports removed in 0.3287 sec])
[Unchanged]     lib/sqlalchemy/orm/strategies.py (in 0.2237 sec)

The program has two general modes of usage. One is that of day-to-day usage for an application that already has clean imports. Running zimports on the source files of such an application should produce no changes, except for whatever source files were recently edited, and may have some changes to imports that need to be placed into the correct order. This usage model is similar to that of Black, where you can run “zimports .” and it will find whatever files need adjusting and leave the rest alone.

The other mode of usage is that of the up-front cleaning up of an application that has un- organized imports. In this mode of usage, the goal is to get the source files to be cleaned up so that zimports can be run straight without any modifications to the file needed, including that all necessary imports are either used locally or marked as not to be removed.

Problems that can occur during this phase are that some imports are unused and should be removed, while other imports that are apparently unused are still in fact imported by other parts of the program. Another issue is that changing the ordering of imports in complex cases may cause the application to no longer run due to the creation of unresolvable import cycles. Finally, some programs have use of import *, pulling in a large list of names for which an unknown portion of them are needed by the application. The options --keep-unused, --heuristic-unused and --expand-stars are provided to assist in working through these issues until the code can be fully reformatted such that running zimports no longer produces changes.

The issue of apparently unused imports that are externally imported can be prominent in some applications. In order to allow imports that aren’t locally used to remain in the source file, symbols that are part of __all__ will not be removed, as will imports that are followed by a `` # noqa`` comment. Either of these techniques should be applied to imports that are used from other modules but not otherwise referenced within the immediate source file. For the less common case that a few imports really need a very specific import order for things to work, those imports can be followed by a `` # noqa nosort`` comment that will add these lines to a special group at the end of all imports, where they will not be removed and their order relative to each other will be maintained.

The program does currently require that you pass it at least one file or directory name as an argument. It also does not have the file caching feature that Black has, which can allow it to only look at files that have changed since the last run. The plan is to have it check that it’s inside a git repository where it will run through files to be committed if no filenames are given.

Usage as a git hook

zimports can be used with the pre-commit git hooks framework. To add the plugin, add the following to your .pre-commit-config.yaml. Note the rev: attribute refers to a git tag or revision number of zimports to be used, such as "master" or "0.1.3":

repos:
-   repo: https://github.com/sqlalchemyorg/zimports/
    rev: 0.1.3
    hooks:
    -   id: zimports