Consistency

These checks limit the Python’s inconsistency.

We can do the same things differently in Python. For example, there are three ways to format a string. There are several ways to write the same number.

We like our code to be consistent. It is easier to bare with your code base if you follow these rules.

So, we choose a single way to do things. It does not mean that we choose the best way to do it. But, we value consistency more than being 100% right. And we are ready to suffer all trade-offs that might come.

Once again, these rules are highly subjective. But, we love them.

Summary

LocalFolderImportViolation	Forbids to have imports relative to the current folder.
DottedRawImportViolation	Forbids to use imports like import os.path.
UnicodeStringViolation	Forbids to use u string prefix.
UnderscoredNumberViolation	Forbids to use underscores (_) in numbers.
PartialFloatViolation	Forbids to use partial floats like .05 or 23..
FormattedStringViolation	Forbids to use f strings.
RequiredBaseClassViolation	Forbids to write classes without base classes.
MultipleIfsInComprehensionViolation	Forbids to have multiple if statements inside list comprehensions.
ConstantComparisonViolation	Forbids to have comparisons between two literals.
ComparisonOrderViolation	Forbids comparision where argument doesn’t come first.
BadNumberSuffixViolation	Forbids to use capital X, O, B, and E in numbers.
MultipleInComparisonViolation	Forbids comparision where multiple in checks.
RedundantComparisonViolation	Forbids to have comparisons between the same variable.
MissingSpaceBetweenKeywordAndParenViolation	Enforces to separate parenthesis from the keywords with spaces.
WrongConditionalViolation	Forbids using if statements that use invalid conditionals.
ObjectInBaseClassesListViolation	Forbids extra object in parent classes list.
MultipleContextManagerAssignmentsViolation	Forbids multiple assignment targets for context managers.
ParametersIndentationViolation	Forbids to use incorrect parameters indentation.
ExtraIndentationViolation	Forbids to use extra indentation.
WrongBracketPositionViolation	Forbids to use extra indentation.
MultilineFunctionAnnotationViolation	Forbids to use multi-line function type annotations.
UppercaseStringModifierViolation	Forbids to use uppercase string modifiers.
IncorrectMultilineStringViolation	Forbids to use triple quotes for singleline strings.
EmptyLineAfterCodingViolation	Enforces to have an extra empty line after the coding comment.
InconsistentReturnViolation	Enforces to have consistent return statements.
InconsistentYieldViolation	Enforces to have consistent yield statements.
ImplicitStringConcatenationViolation	Forbids to use implicit string contacatenation.
UselessContinueViolation	Forbids to use meaningless continue node in loops.
UselessNodeViolation	Forbids to use meaningless nodes.
UselessExceptCaseViolation	Forbids to use meaningless except cases.

Consistency checks

class LocalFolderImportViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to have imports relative to the current folder.

Reasoning:

We should pick one style and stick to it. We have decided to use the explicit one.

Solution:

Refactor your imports to use the absolute path.

Example:

# Correct:
from my_package.version import get_version

# Wrong:
from .version import get_version
from ..drivers import MySQLDriver

New in version 0.1.0.

error_template = 'Found local folder import'

code = 300

class DottedRawImportViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to use imports like import os.path.

Reasoning:

There too many different ways to import something. We should pick one style and stick to it. We have decided to use the readable one.

Solution:

Refactor your import statement.

Example:

# Correct:
from os import path

# Wrong:
import os.path

New in version 0.1.0.

error_template = 'Found dotted raw import: {0}'

code = 301

class UnicodeStringViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.TokenizeViolation

Forbids to use u string prefix.

Reasoning:

We do not need this prefix since python2. But, it is still possible to find it inside the codebase.

Solution:

Remove this prefix.

Example:

# Correct:
nickname = 'sobolevn'
file_contents = b'aabbcc'

# Wrong:
nickname = u'sobolevn'

New in version 0.1.0.

code = 302

error_template = 'Found unicode string prefix: {0}'

class UnderscoredNumberViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.TokenizeViolation

Forbids to use underscores (_) in numbers.

Reasoning:

It is possible to write 1000 in three different ways: 1_000, 10_00, and 100_0. And it would be still the same number. Count how many ways there are to write bigger numbers. Currently, it all depends on the cultural habits of the author. We enforce a single way to write numbers: without the underscore.

Solution:

Numbers should be written as numbers: 1000. If you have a very big number with a lot of zeros, use multiplication.

Example:

# Correct:
phone = 88313443
million = 1000000

# Wrong:
phone = 8_83_134_43
million = 100_00_00

New in version 0.1.0.

code = 303

error_template = 'Found underscored number: {0}'

class PartialFloatViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.TokenizeViolation

Forbids to use partial floats like .05 or 23..

Reasoning:

Partial numbers are hard to read and they can be confused with other numbers. For example, it is really easy to confuse 0.5 and .05 when reading through the source code.

Solution:

Use full versions with leading and starting zeros.

Example:

# Correct:
half = 0.5
ten_float = 10.0

# Wrong:
half = .5
ten_float = 10.

New in version 0.1.0.

code = 304

error_template = 'Found partial float: {0}'

class FormattedStringViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to use f strings.

Reasoning:

f strings loses context too often and they are hard to lint. Imagine that you have a string that breaks when you move it two lines above. That’s not how a string should behave. Also, they promote a bad practice: putting your logic inside the template.

Solution:

Use .format() with indexed params instead.

See also

https://github.com/xZise/flake8-string-format

Example:

# Wrong:
f'Result is: {2 + 2}'

# Correct:
'Result is: {0}'.format(2 + 2)
'Hey {user}! How are you?'.format(user='sobolevn')

New in version 0.1.0.

error_template = 'Found `f` string'

code = 305

class RequiredBaseClassViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to write classes without base classes.

Reasoning:

We just need to decide how to do it. We need a single and unified rule about base classes. We have decided to stick to the explicit base class notation.

Solution:

Add a base class.

Example:

# Correct:
class Some(object): ...

# Wrong:
class Some: ...

New in version 0.1.0.

error_template = 'Found class without a base class: {0}'

code = 306

class MultipleIfsInComprehensionViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to have multiple if statements inside list comprehensions.

Reasoning:

It is very hard to read multiple if statements inside a list comprehension. Since it is even hard to tell all of them should pass or fail.

Solution:

Use a single if statement inside list comprehensions. Use filter() if you have complicated logic.

Example:

# Wrong:
nodes = [node for node in html if node != 'b' if node != 'i']

# Correct:
nodes = [node for node in html if node not in ('b', 'i')]

New in version 0.1.0.

error_template = 'Found list comprehension with multiple `if`s'

code = 307

class ConstantComparisonViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to have comparisons between two literals.

Reasoning:

When two constants are compared it is typically an indication of a mistake, since the Boolean value of the comparison, will always be the same.

Solution:

Remove the constant comparison and any associated dead code.

Example:

# Wrong:
if 60 * 60 < 1000:
    do_something()
else:
    do_something_else()

# Correct:
do_something_else()

New in version 0.3.0.

error_template = 'Found constant comparison'

code = 308

class ComparisonOrderViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids comparision where argument doesn’t come first.

Reasoning:

It is hard to read the code when you have to shuffle ordering of the arguments all the time. Bring consistency to the comparison!

Solution:

Refactor your comparison expression, place the argument first.

Example:

# Correct:
if some_x > 3:
if 3 < some_x < 10:

# Wrong:
if 3 < some_x:

New in version 0.3.0.

error_template = 'Found reversed comparison order'

code = 309

class BadNumberSuffixViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.TokenizeViolation

Forbids to use capital X, O, B, and E in numbers.

Reasoning:

Octal, hex, binary and scientific notation suffixes could be written in two possible notations: lowercase and uppercase. Which brings confusion and decreases code consistency and readability. We enforce a single way to write numbers with suffixes: suffix with lowercase chars.

Solution:

Octal, hex, binary and scientific notation suffixes in numbers should be written lowercase.

Example:

# Correct:
hex_number = 0xFF
octal_number = 0o11
binary_number = 0b1001
number_with_scientific_notation = 1.5e+10

# Wrong:
hex_number = 0XFF
octal_number = 0O11
binary_number = 0B1001
number_with_scientific_notation = 1.5E+10

New in version 0.3.0.

error_template = 'Found bad number suffix: {0}'

code = 310

class MultipleInComparisonViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids comparision where multiple in checks.

Reasoning:

Using multiple in is unreadable.

Solution:

Refactor your comparison expression to use several and conditions or separate if statements in case it is appropriate.

Example:

# Correct:
if item in bucket and bucket in master_list_of_buckets:
if x_coord in line and line in square:

# Wrong:
if item in bucket in master_list_of_buckets:
if x_cord in line in square:

New in version 0.3.0.

error_template = 'Found multiple `in` comparisons'

code = 311

class RedundantComparisonViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to have comparisons between the same variable.

Reasoning:

When the same variables are compared it is typically an indication of a mistake, since the Boolean value of the comparison will always be the same.

Solution:

Remove the same variable comparison and any associated dead code.

Example:

# Wrong:
a = 1
if a < a:
    do_something()
else:
    do_something_else()

# Correct:
do_something()

New in version 0.3.0.

error_template = 'Found comparison between same variable'

code = 312

class MissingSpaceBetweenKeywordAndParenViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.TokenizeViolation

Enforces to separate parenthesis from the keywords with spaces.

Reasoning:

Some people use return and yield keywords as functions. The same happened to good old print in Python2.

Solution:

Insert space symbol between keyword and open paren.

Example:

# Wrong:
def func():
    a = 1
    b = 2
    del(a, b)
    yield(1, 2, 3)

# Correct:
def func():
    a = 1
    del (a, b)
    yield (1, 2, 3)

New in version 0.3.0.

error_template = 'Found parens right after a keyword'

code = 313

class WrongConditionalViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids using if statements that use invalid conditionals.

Reasoning:

When invalid conditional arguments are used it is typically an indication of a mistake, since the value of the conditional result will always be the same.

Solution:

Remove the conditional and any associated dead code.

Example:

# Correct:
if value is True: ...

# Wrong:
if True: ...

New in version 0.3.0.

error_template = 'Conditional always evaluates to same result'

code = 314

class ObjectInBaseClassesListViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids extra object in parent classes list.

Reasoning:

We should allow object only when we explicitly use it as a single parent class. When there is another class or there are multiple parents - we should not allow it for the consistency reasons.

Solution:

Remove extra object parent class from the list.

Example:

# Correct:
class SomeClassName(object): ...
class SomeClassName(FirstParentClass, SecondParentClass): ...

# Wrong:
class SomeClassName(FirstParentClass, SecondParentClass, object): ...

New in version 0.3.0.

error_template = 'Founded extra `object` in parent classes list'

code = 315

class MultipleContextManagerAssignmentsViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids multiple assignment targets for context managers.

Reasoning:

It is hard to distinguish whether as should unpack into tuple or we are just using two context managers.

Solution:

Use several context managers. Or explicit brackets.

Example:

# Correct:
with open('') as first:
    with second:
        ...

with some_context as (first, second):
    ...

# Wrong:
with open('') as first, second:
    ...

New in version 0.6.0.

error_template = 'Found context manager with too many assignments'

code = 316

class ParametersIndentationViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to use incorrect parameters indentation.

Reasoning:

It is really easy to spoil your perfect, readable code with incorrect multi-line parameters indentation. Since it is really easy to style them in any of 100 possible ways. We enforce a strict rule about how it is possible to write these multi-line parameters.

Solution:

Use consistent multi-line parameters indentation.

Example:

# Correct:
def my_function(arg1, arg2, arg3) -> None:
    return None

print(1, 2, 3, 4, 5, 6)

def my_function(
    arg1, arg2, arg3,
) -> None:
    return None

print(
    1, 2, 3, 4, 5, 6,
)

def my_function(
    arg1,
    arg2,
    arg3,
) -> None:
    return None

print(
    first_variable,
    2,
    third_value,
    4,
    5,
    last_item,
)

# Special case:

print('some text', 'description', [
    first_variable,
    second_variable,
    third_variable,
    last_item,
], end='')

Everything else is considered a violation. This rule checks: lists, sets, tuples, dicts, calls, functions, methods, and classes.

New in version 0.6.0.

error_template = 'Found incorrect multi-line parameters'

code = 317

class ExtraIndentationViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.TokenizeViolation

Forbids to use extra indentation.

Reasoning:

You can use extra indentation for lines of code. Python allows you to do that in case you will keep the indentation level equal for this specific node. But, that’s insane!

Solution:

We should stick to 4 spaces for an indentation block. Each next block should be indented by just 4 extra spaces.

Example:

# Correct:
def test():
    print('test')

# Wrong:
def test():
            print('test')

New in version 0.6.0.

error_template = 'Found extra indentation'

code = 318

class WrongBracketPositionViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.TokenizeViolation

Forbids to use extra indentation.

Reasoning:

You can use extra indentation for lines of code. Python allows you to do that in case you will keep the indentation level equal for this specific node. But, that’s insane!

Solution:

Place bracket on the same line, when a single line expression. Or place the bracket on a new line when a multi-line expression.

Example:

# Correct:
print([
    1, 2, 3,
])

print(
    1,
    2,
)

def _annotate_brackets(
    tokens: List[tokenize.TokenInfo],
) -> TokenLines:
    ...

# Wrong:
print([
    1, 2, 3],
)

print(
    1,
    2)

def _annotate_brackets(
    tokens: List[tokenize.TokenInfo]) -> TokenLines:
    ...

We check round, square, and curly brackets.

New in version 0.6.0.

error_template = 'Found bracket in wrong position'

code = 319

class MultilineFunctionAnnotationViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to use multi-line function type annotations.

Reasoning:

Functions with multi-line type annotations are unreadable.

Solution:

Use type annotations that fit into a single line to annotate functions. If your annotation is too long, then use type aliases.

Example:

# Correct:
def create_list(length: int) -> List[int]:
    ...

# Wrong:
def create_list(length: int) -> List[
    int,
]:
    ...

This rule checks argument and return type annotations.

New in version 0.6.0.

error_template = 'Found multi-line function type annotation'

code = 320

class UppercaseStringModifierViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.TokenizeViolation

Forbids to use uppercase string modifiers.

Reasoning:

String modifiers should be consistent.

Solution:

Use lowercase modifiers should be written in lowercase.

Example:

# Correct:
some_string = r'/regex/'
some_bytes = b'123'

# Wrong:
some_string = R'/regex/'
some_bytes = B'123'

New in version 0.6.0.

error_template = 'Found uppercase string modifier: {0}'

code = 321

class IncorrectMultilineStringViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.TokenizeViolation

Forbids to use triple quotes for singleline strings.

Reasoning:

String quotes should be consistent.

Solution:

Use single quotes for single-line strings. Triple quotes are only allowed for real multiline strings.

Example:

# Correct:
single_line = 'abc'
multiline = """
    one
    two
"""

# Wrong:
some_string = """abc"""
some_bytes = b"""123"""

Docstrings are ignored from this rule. You must use triple quotes strings for docstrings.

New in version 0.7.0.

error_template = 'Found incorrect multi-line string'

code = 322

class EmptyLineAfterCodingViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.TokenizeViolation

Enforces to have an extra empty line after the coding comment.

Reasoning:

This is done for pure consistency.

Solution:

Add an empty line between coding magic comment and your code.

Example:

# Correct:
# coding: utf-8

SOME_VAR = 1

# Wrong:
# coding: utf-8
SOME_VAR = 1

New in version 0.7.0.

error_template = 'Found missing empty line between `coding` magic comment and code'

code = 323

class InconsistentReturnViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.ASTViolation

Enforces to have consistent return statements.

Rules are: 1. if any return has a value, all return nodes should have a value 2. do not place return without value at the end of a function

This rule respects mypy style of placing return statements. There should be no conflict with these two checks.

Reasoning:

This is done for pure consistency and readability of your code. Eventually, this rule may also find some bugs in your code.

Solution:

Add or remove values from the return statements to make them consistent. Remove return statement from the function end.

Example:

# Correct:
def function():
    if some:
        return 2
    return 1

# Wrong:
def function():
    if some:
        return
    return 1

def function():
    if some:
        print(some)
    return

New in version 0.7.0.

error_template = 'Found inconsistent `return` statement'

code = 324

class InconsistentYieldViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.ASTViolation

Enforces to have consistent yield statements.

Rules are: 1. if any yield has a value, all yield nodes should have a value

This rule respects mypy style of placing yield statements. There should be no conflict with these two checks.

Reasoning:

This is done for pure consistency and readability of your code. Eventually, this rule may also find some bugs in your code.

Solution:

Add or remove values from the yield statements to make them consistent.

Example:

# Correct:
def function():
    if some:
        yield 2
    yield 1

# Wrong:
def function():
    if some:
        yield
    yield 1

New in version 0.7.0.

error_template = 'Found inconsistent `yield` statement'

code = 325

class ImplicitStringConcatenationViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.TokenizeViolation

Forbids to use implicit string contacatenation.

Reasoning:

This is error-prone, since you can possible miss a comma in a collection of string and get an implicit concatenation. And because there are different and safe ways to do the same thing it is better to use them instead.

Solution:

Use + or .format() to join strings.

Example:

# Correct:
text = 'first' + 'second'

# Wrong:
text = 'first' 'second'

New in version 0.7.0.

error_template = 'Found implicit string concatenation'

code = 326

class UselessContinueViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to use meaningless continue node in loops.

Reasoning:

Placing this keyword in the end of any loop won’t make any difference to your code. And we prefer not to have meaningless constructs in our code.

Solution:

Remove useless continue node from the loop.

Example:

# Correct:
for number in [1, 2, 3]:
    if number < 2:
        continue
    print(number)

# Wrong:
for number in [1, 2, 3]:
    print(number)
    continue

New in version 0.7.0.

error_template = 'Found useless `continue` at the end of the loop'

code = 327

class UselessNodeViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to use meaningless nodes.

Reasoning:

Some nodes might be completely useless. They will literally do nothing. Sometimes they are hard to find, because this situation can be caused by a recent refactoring or just by acedent. This might be also an overuse of syntax.

Solution:

Remove node or make sure it makes any sense.

Example:

# Wrong:
for number in [1, 2, 3]:
    break

New in version 0.7.0.

error_template = 'Found useless node: {0}'

code = 328

class UselessExceptCaseViolation(node, text=None)

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to use meaningless except cases.

Reasoning:

Using except cases that just reraise the same exception is error-prone. You can increase your stacktrace, silence some potential exceptions, and screw things up. It also does not make any sense to do so.

Solution:

Remove except case or make sure it makes any sense.

Example:

# Correct:
try:
    ...
except IndexError:
    sentry.log()
    raise ValueError()

# Wrong:
try:
    ...
except TypeError:
    raise

New in version 0.7.0.

error_template = 'Found useless `except` case'

code = 329