Source code for wemake_python_styleguide.violations.best_practices
# -*- coding: utf-8 -*-
"""
These checks ensures that you follow the best practices.
Note:
Explicit is better than implicit.
Simple is better than complex.
Complex is better than complicated.
Readability counts.
Special cases aren't special enough to break the rules.
In the face of ambiguity, refuse the temptation to guess.
There should be one-- and preferably only one --obvious way to do it.
.. currentmodule:: wemake_python_styleguide.violations.best_practices
Summary
-------
.. autosummary::
:nosignatures:
WrongMagicCommentViolation
WrongDocCommentViolation
WrongModuleMetadataViolation
EmptyModuleViolation
InitModuleHasLogicViolation
WrongKeywordViolation
WrongFunctionCallViolation
FutureImportViolation
RaiseNotImplementedViolation
NestedFunctionViolation
NestedClassViolation
MagicNumberViolation
StaticMethodViolation
BadMagicMethodViolation
NestedImportViolation
Comments
--------
.. autoclass:: WrongMagicCommentViolation
.. autoclass:: WrongDocCommentViolation
Modules
-------
.. autoclass:: WrongModuleMetadataViolation
.. autoclass:: EmptyModuleViolation
.. autoclass:: InitModuleHasLogicViolation
Builtins
--------
.. autoclass:: WrongKeywordViolation
.. autoclass:: WrongFunctionCallViolation
.. autoclass:: FutureImportViolation
.. autoclass:: RaiseNotImplementedViolation
Design
------
.. autoclass:: NestedFunctionViolation
.. autoclass:: NestedClassViolation
.. autoclass:: MagicNumberViolation
.. autoclass:: StaticMethodViolation
.. autoclass:: BadMagicMethodViolation
.. autoclass:: NestedImportViolation
"""
from wemake_python_styleguide.violations.base import (
ASTViolation,
SimpleViolation,
TokenizeViolation,
)
# Modules:
[docs]class EmptyModuleViolation(ASTViolation):
"""
Forbids to have empty modules.
Reasoning:
Why is it even there? Do not polute your project with empty files.
Solution:
If you have an empty module there are two ways to handle that:
1. delete it
2. drop some documentation in it, so you will explain why it is there
Note:
Returns Z411 as error code
"""
should_use_text = False
#: Error message shown to the user.
error_template = 'Found empty module'
code = 411
[docs]class InitModuleHasLogicViolation(ASTViolation):
"""
Forbids to have logic inside ``__init__`` module.
Reasoning:
If you have logic inside the ``__init__`` module
it means several things:
1. you are keeping some outdated stuff there, you need to refactor
2. you are placing this logic into the wrong file,
just create another one
3. you are doing some dark magic, and you should not do that
Solution:
Put your code in other modules.
However, we allow to have some contents inside the ``__init__`` module:
1. comments, since they are dropped before AST comes in play
2. docs string, because sometimes it is required to state something
Note:
Returns Z412 as error code
"""
should_use_text = False
#: Error message shown to the user.
error_template = 'Found `__init__` module with logic'
code = 412
# Modules:
[docs]class WrongKeywordViolation(ASTViolation):
"""
Forbids to use some keywords from ``python``.
Reasoning:
We believe that some keywords are anti-patterns.
They promote bad-practices like ``global`` and ``pass``,
or just not user-friendly like ``del``.
Solution:
Solutions differ from keyword to keyword.
``pass`` should be replaced with docstring or ``contextlib.suppress``.
``del`` should be replaced with specialized methods like ``.pop()``.
``global`` and ``nonlocal`` usages should be refactored.
Example::
# Wrong:
pass
del
nonlocal
global
Note:
Returns Z420 as error code
"""
#: Error message shown to the user.
error_template = 'Found wrong keyword "{0}"'
code = 420
[docs]class WrongFunctionCallViolation(ASTViolation):
"""
Forbids to call some built-in functions.
Reasoning:
Some functions are only suitable
for very specific use cases,
we forbid to use them in a free manner.
See
:py:data:`~wemake_python_styleguide.constants.BAD_FUNCTIONS`
for the full list of blacklisted functions.
See also:
https://www.youtube.com/watch?v=YjHsOrOOSuI
Note:
Returns Z421 as error code
"""
#: Error message shown to the user.
error_template = 'Found wrong function call "{0}"'
code = 421
[docs]class FutureImportViolation(ASTViolation):
"""
Forbids to use ``__future__`` imports.
Reasoning:
Almost all ``__future__`` imports are legacy ``python2`` compatibility
tools that are no longer required.
Solution:
Remove them. Drop ``python2`` support.
Except, there are some new ones for ``python4`` support.
See
:py:data:`~wemake_python_styleguide.constants.FUTURE_IMPORTS_WHITELIST`
for the full list of allowed future imports.
Example::
# Correct:
from __future__ import annotations
# Wrong:
from __future__ import print_function
Note:
Returns Z422 as error code
"""
#: Error message shown to the user.
error_template = 'Found future import "{0}"'
code = 422
[docs]class RaiseNotImplementedViolation(ASTViolation):
"""
Forbids to use ``NotImplemented`` error.
Reasoning:
These two violations look so similar.
But, these violations have different use cases.
Use cases of ``NotImplemented`` is too limited
to be generally available.
Solution:
Use ``NotImplementedError``.
Example::
# Correct:
raise NotImplementedError('To be done')
# Wrong:
raise NotImplemented
See Also:
https://stackoverflow.com/a/44575926/4842742
Note:
Returns Z423 as error code
"""
should_use_text = False
#: Error message shown to the user.
error_template = 'Found raise NotImplemented'
code = 423
# Design:
[docs]class NestedFunctionViolation(ASTViolation):
"""
Forbids to have nested functions.
Reasoning:
Nesting functions is a bad practice.
It is hard to test them, it is hard then to separate them.
People tend to overuse closures, so it's hard to manage the dataflow.
Solution:
Just write flat functions, there's no need to nest them.
Pass parameters as normal arguments, do not use closures.
Until you need them for decorators or factories.
We also disallow to nest ``lambda`` and ``async`` functions.
See
:py:data:`~wemake_python_styleguide.constants.NESTED_FUNCTIONS_WHITELIST`
for the whole list of whitelisted names.
Example::
# Correct:
def do_some(): ...
def other(): ...
# Wrong:
def do_some():
def inner():
...
Note:
Returns Z430 as error code
"""
#: Error message shown to the user.
error_template = 'Found nested function "{0}"'
code = 430
[docs]class NestedClassViolation(ASTViolation):
"""
Forbids to use nested classes.
Reasoning:
Nested classes are really hard to manage.
You can not even create an instance of this class in many cases.
Testing them is also really hard.
Solution:
Just write flat classes, there's no need nest them.
If you are nesting classes inside a function for parametrization,
then you will probably need to use different design (or metaclasses).
See
:py:data:`~wemake_python_styleguide.constants.NESTED_CLASSES_WHITELIST`
for the full list of whitelisted names.
Example::
# Correct:
class Some(object): ...
class Other(object): ...
# Wrong:
class Some(object):
class Inner(object):
...
Note:
Returns Z431 as error code
"""
#: Error message shown to the user.
error_template = 'Found nested class "{0}"'
code = 431
[docs]class MagicNumberViolation(ASTViolation):
"""
Forbids to use magic numbers in your code.
What we call a "magic number"? Well, it is actually any number that
appears in your code out of nowhere. Like ``42``. Or ``0.32``.
Reasoning:
It is very hard to remember what these numbers actually mean.
Why were they used? Should they ever be changed?
Or are they eternal like ``3.14``?
Solution:
Give these numbers a name! Move them to a separate variable,
giving more context to the reader. And by moving things into new
variables you will trigger other complexity checks.
Example::
# Correct:
price_in_euro = 3.33 # could be changed later
total = get_items_from_cart() * price_in_euro
# Wrong:
total = get_items_from_cart() * 3.33
What are numbers that we exclude from this check?
Any numbers that are assigned to a variable, array, dictionary,
or keyword arguments inside a function.
``int`` numbers that are in range ``[-10, 10]`` and
some other common numbers, that are defined in
:py:data:`~wemake_python_styleguide.constants.MAGIC_NUMBERS_WHITELIST`
See also:
https://en.wikipedia.org/wiki/Magic_number_(programming)
Note:
Returns Z432 as error code
"""
code = 432
#: Error message shown to the user.
error_template = 'Found magic number: {0}'
[docs]class StaticMethodViolation(ASTViolation):
"""
Forbids to use ``@staticmethod`` decorator.
Reasoning:
Static methods are not required to be inside the class.
Because they even do not have access to the current instance.
Solution:
Use instance methods, ``@classmethod``, or functions instead.
Note:
Returns Z433 as error code
"""
should_use_text = False
#: Error message shown to the user.
error_template = 'Found using `@staticmethod`'
code = 433
[docs]class BadMagicMethodViolation(ASTViolation):
"""
Forbids to use some magic methods.
Reasoning:
We forbid to use magic methods related to the forbidden language parts.
Likewise, we forbid to use ``del`` keyword, so we forbid to use all
magic methods related to it.
Solution:
Refactor you code to use custom methods instead.
It will give more context to your app.
See
:py:data:`~wemake_python_styleguide.constants.BAD_MAGIC_METHODS`
for the full blacklist of the magic methods.
See also:
https://www.youtube.com/watch?v=F6u5rhUQ6dU
Note:
Returns Z434 as error code
"""
#: Error message shown to the user.
error_template = 'Found using restricted magic method "{0}"'
code = 434
[docs]class NestedImportViolation(ASTViolation):
"""
Forbids to have nested imports in functions.
Reasoning:
Usually nested imports are used to fix the import cycle.
So, nested imports show that there's an issue with you design.
Solution:
You don't need nested imports, you need to refactor your code.
Introduce a new module or find another way to do what you want to do.
Rethink how your layered architecture should look like.
Example::
# Correct:
from my_module import some_function
def some(): ...
# Wrong:
def some():
from my_module import some_function
See also:
https://github.com/seddonym/layer_linter
Note:
Returns Z435 as error code
"""
#: Error message shown to the user.
error_template = 'Found nested import "{0}"'
code = 435