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.

ConstantCompareViolation

Forbids to have compares between two literals.

CompareOrderViolation

Forbids comparision where argument doesn’t come first.

BadNumberSuffixViolation

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

MultipleInCompareViolation

Forbids comparision where multiple in checks.

UselessCompareViolation

Forbids to have compares between the same variable.

MissingSpaceBetweenKeywordAndParenViolation

Enforces to separate parenthesis from the keywords with spaces.

ConstantConditionViolation

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 have brackets in the wrong position.

MultilineFunctionAnnotationViolation

Forbids to use multi-line function type annotations.

UppercaseStringModifierViolation

Forbids to use uppercase string modifiers.

WrongMultilineStringViolation

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.

UselessOperatorsViolation

Forbids the use of unnecessary operators in your code.

InconsistentReturnVariableViolation

Forbids local variable that are only used in return statements.

ImplicitTernaryViolation

Forbids to have implicit ternary expressions.

ImplicitComplexCompareViolation

Forbids to have implicit complex compare expressions.

ReversedComplexCompareViolation

Forbids to have reversed order complex compare expressions.

WrongLoopIterTypeViolation

Forbids to use wrong for loop iter targets.

ExplicitStringConcatViolation

Forbids explicit string concat in favour of .format method.

MultilineConditionsViolation

Forbids multiline conditions.

WrongMethodOrderViolation

Forbids to have incorrect order of methods inside a class.

NumberWithMeaninglessZeroViolation

Forbids to use meaningless zeros.

PositiveExponentViolation

Forbids to extra + signs in the exponent.

WrongHexNumberCaseViolation

Forbids use lower-case letters as hex numbers.

ImplicitRawStringViolation

Forbids to use \\ escape sequences inside regular strings.

BadComplexNumberSuffixViolation

Forbids to use uppercase complex number suffix.

ZeroDivisionViolation

Forbids to explicitly divide by zero.

MeaninglessNumberOperationViolation

Forbids to use meaningless math opeartions with 0 and 1.

OperationSignNegationViolation

Forbids to have double minus operations.

Consistency checks

class LocalFolderImportViolation(node, text=None)[source]

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)[source]

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)[source]

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)[source]

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)[source]

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)[source]

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.

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)[source]

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)[source]

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 ConstantCompareViolation(node, text=None)[source]

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to have compares between two literals.

Reasoning:

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

Solution:

Remove the constant compare 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 compare'
code = 308
class CompareOrderViolation(node, text=None)[source]

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 compare!

Solution:

Refactor your compare 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 compare order'
code = 309
class BadNumberSuffixViolation(node, text=None)[source]

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 MultipleInCompareViolation(node, text=None)[source]

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids comparision where multiple in checks.

Reasoning:

Using multiple in is unreadable.

Solution:

Refactor your compare 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 not in line and line not in square:

# Wrong:
if item in bucket in master_list_of_buckets:
if x_cord not in line not in square:

New in version 0.3.0.

Changed in version 0.10.0.

error_template = 'Found multiple `in` compares'
code = 311
class UselessCompareViolation(node, text=None)[source]

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to have compares 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 compare will always be the same.

Solution:

Remove the same variable compare 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 compare between same variable'
code = 312
class MissingSpaceBetweenKeywordAndParenViolation(node, text=None)[source]

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 ConstantConditionViolation(node, text=None)[source]

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)[source]

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)[source]

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)[source]

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)[source]

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)[source]

Bases: wemake_python_styleguide.violations.base.TokenizeViolation

Forbids to have brackets in the wrong position.

Reasoning:

You can do bizzare things with bracket positioning in python. We require all brackets to be consistent.

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)[source]

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)[source]

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 WrongMultilineStringViolation(node, text=None)[source]

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)[source]

Bases: wemake_python_styleguide.violations.base.TokenizeViolation

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

Reasoning:

Since we use flake8-coding as a part of our linter we care about extra space after this coding comment. This is done for pure consistency.

Why should we even care about this magic coding comment? For several reasons.

First, explicit encoding is always better that an implicit one, different countries still use some non utf-8 encodings as a default. But, people might override it with other encodings in a comment. Do you know how much pain it can cause to you?

We still know that python3 uses utf-8 inside.

Second, some tools break because of this incorrect encoding comment. Including, django, flake8, and tokenize core module. It is very hard to notice these things when they happen.

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)[source]

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

New in version 0.7.0.

error_template = 'Found inconsistent `return` statement'
code = 324
class InconsistentYieldViolation(node, text=None)[source]

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)[source]

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)[source]

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)[source]

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)[source]

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
class UselessOperatorsViolation(node, text=None)[source]

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids the use of unnecessary operators in your code.

You can write: 5.4 and +5.4. There’s no need to use the second version. Similarly --5.4, ---5.4, not not foo, and ~~42 contain unnecessary operators.

Reasoning:

This is done for consistency reasons.

Solution:

Omit unnecessary operators.

Example:

# Correct:
profit = 3.33
profit = -3.33
inverse = ~5
complement = not foo

# Wrong:
profit = +3.33
profit = --3.33
profit = ---3.33
number = ~~42
bar = not not foo

New in version 0.8.0.

code = 330
error_template = 'Found unnecessary operator: {0}'
class InconsistentReturnVariableViolation(node, text=None)[source]

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids local variable that are only used in return statements.

Reasoning:

This is done for consistency and more readable source code.

Solution:

Return the expression itself, instead of creating a temporary variable.

Example:

# Correct:
def some_function():
    return 1

# Wrong:
def some_function():
    some_value = 1
    return some_value

New in version 0.9.0.

error_template = 'Found local variable that are only used in `return` statements'
code = 331
class ImplicitTernaryViolation(node, text=None)[source]

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to have implicit ternary expressions.

Reasoning:

This is done for consistency and readability reasons. We believe that explicit ternary is better for readability. This also allows you to identify hidden conditionals in your code.

Solution:

Refactor to use explicit ternary, or if condition.

Example:

# Correct:
some = one if cond() else two

# Wrong:
some = cond() and one or two

New in version 0.10.0.

code = 332
error_template = 'Found implicit ternary expression'
class ImplicitComplexCompareViolation(node, text=None)[source]

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to have implicit complex compare expressions.

Reasoning:

Two compares in python that are joined with and operator mean that you indeed have a complex compare with tree operators.

Solution:

Refactor your compare without and but with the third operator. Notice, that you migth have to change the ordering.

Example:

# Correct:
if three < two < one:
    ...

# Wrong:
if one > two and two > three:
    ...

New in version 0.10.0.

code = 333
error_template = 'Found implicit complex compare'
class ReversedComplexCompareViolation(node, text=None)[source]

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to have reversed order complex compare expressions.

Reasoning:

Compares where comparators start from the lowest element are easier to read than one that start from the biggest one. It is also possible to write the same expression in two separate way, which is incosistent.

Solution:

Reverse the order, so the smallest element comes the first and the biggest one comes the last.

Example:

# Correct:
if three < two < one:
    ...

# Wrong:
if one > two > three:
    ...

New in version 0.10.0.

code = 334
error_template = 'Found reversed complex compare'
class WrongLoopIterTypeViolation(node, text=None)[source]

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to use wrong for loop iter targets.

We forbid to use:

  • Lists and list comprehensions

  • Sets and set comprehensions

  • Dicts and dict comprehensions

  • Generator expressions

  • Empty tuples

Reasoning:

Using lists, dicts, and sets do not make much sense. You can use tuples instead. Using comprehensions implicitly create a two level loops, that are hard to read and deal with.

Solution:

Use tuples to create explicit iterables for for loops. In case you are using a comprehension, create a new variable.

Example:

# Correct:
for person in ('Kim', 'Nick'):
    ...

# Wrong:
for person in ['Kim', 'Nick']:
    ...

New in version 0.10.0.

Changed in version 0.12.0.

code = 335
error_template = 'Found incorrect `for` loop iter type'
class ExplicitStringConcatViolation(node, text=None)[source]

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids explicit string concat in favour of .format method.

However, we still allow multiline string concat as a way to write long stirngs that does not fit the 80-chars rule.

Reasoning:

When formating strings one must use .format and not any other formatting methods like %, +, or f. This is done for consistency reasons.

Solution:

Join strings together if you can, or use .format method.

Example:

# Correct:
x = 'ab: {0}'.format(some_data)

# Wrong:
x = 'a' + 'b: ' + some_data

New in version 0.12.0.

code = 336
error_template = 'Found explicit string concat'
class MultilineConditionsViolation(node, text=None)[source]

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids multiline conditions.

Reasoning:

This way of writing conditions hides the inner complexity this line has. And it decreases readability of the code.

Solution:

Divide multiline conditions to some if condition. Or use variables.

Example:

# Correct:
if isinstance(node.test, ast.UnaryOp):
    if isinstance(node.test.op, ast.Not):
        ...


# Wrong:
if isinstance(node.test, ast.UnaryOp) and isinstance(
    node.test.op,
    ast.Not,
):
    ...

New in version 0.9.0.

Changed in version 0.11.0.

error_template = 'Found multiline conditions'
code = 337
previous_codes = {465}
class WrongMethodOrderViolation(node, text=None)[source]

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to have incorrect order of methods inside a class.

We follow the same ordering:

  • __new__

  • __init__

  • public and megic methods

  • protected methods

  • private methods (we discourage to use them)

We follow “Newspaper order” when the most important things come the first.

Reasoning:

It is hard to read classes which API declarations is bloated with implementation details. We need to see the important stuff first, then we can go deeper in case we are interested.

Solution:

Reorder methods inside your class to match our format.

New in version 0.12.0.

error_template = 'Found incorrect order of methods in a class'
code = 338
class NumberWithMeaninglessZeroViolation(node, text=None)[source]

Bases: wemake_python_styleguide.violations.base.TokenizeViolation

Forbids to use meaningless zeros.

We discorauge using meaningless zeros in float, binary, octal, hex, and expanentional numbers.

Reasoning:

There are ~infinitive ways to write these numbers by adding meaningless leading zeros to the number itself. 0b1 is the same as 0b01 and 0b001. How a language can be called consistent if you can write numbers in a infinite ways? It hurts readability and understanding of your code.

Solution:

Remove meaningless leading zeros.

Example:

# Correct:
numbers = [1.5, 0b1, 0o2, 0x5, 10e10]

# Wrong:
numbers = [1.50, 0b00000001, 0o0002, 0x05, 10e010]

New in version 0.12.0.

error_template = 'Found number with meaningless zeros: {0}'
code = 339
class PositiveExponentViolation(node, text=None)[source]

Bases: wemake_python_styleguide.violations.base.TokenizeViolation

Forbids to extra + signs in the exponent.

Reasoning:

Positive exponent is positive by default, there’s no need to write an extra + sign. We enforce consistency with this rule.

Solution:

Remove meaningless + sign from the exponent.

Example:

# Correct:
number = 1e1 + 1e-1

# Wrong:
number = 1e+1

New in version 0.12.0.

error_template = 'Found exponent number with positive exponent: {0}'
code = 340
class WrongHexNumberCaseViolation(node, text=None)[source]

Bases: wemake_python_styleguide.violations.base.TokenizeViolation

Forbids use lower-case letters as hex numbers.

Reasoning:

One can write 0xA and 0xa which is inconsistent. This rule enforces upper-case letters in hex numbers.

Solution:

Use upper-case letters in hex numbers.

Example:

# Correct:
number = 0xABCDEF

# Wrong:
number = 0xabcdef

New in version 0.12.0.

error_template = 'Found wrong hex number case: {0}'
code = 341
class ImplicitRawStringViolation(node, text=None)[source]

Bases: wemake_python_styleguide.violations.base.TokenizeViolation

Forbids to use \\ escape sequences inside regular strings.

Reasoning:

It is hard to read escape sequencse inside regular strings, because they use \\ double backslash for a single character escape.

Solution:

Use raw strings r'' to rewrite the escape sequence with a \ single backslash.

Example:

# Correct:
escaped = [r'\n', '\n']

# Wrong:
escaped = '\\n'

New in version 0.12.0.

error_template = 'Found implicit raw string: {0}'
code = 342
class BadComplexNumberSuffixViolation(node, text=None)[source]

Bases: wemake_python_styleguide.violations.base.TokenizeViolation

Forbids to use uppercase complex number suffix.

Reasoning:

Numbers should be consistent.

Solution:

Use lowercase suffix for imaginary part.

Example:

# Correct:
complex_number = 1j

# Wrong:
complex_number = 1J

New in version 0.12.0.

error_template = 'Found wrong complex number suffix: {0}'
code = 343
class ZeroDivisionViolation(node, text=None)[source]

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to explicitly divide by zero.

Reasoning:

This will just throw ZeroDivisoionError in case that’s what you need: just throw it. No need to use undefined meth behaviours. Or it might be just a typo / mistake, then fix it.

Solution:

Use ZeroDivisoionError or fix your number not to be 0.

Example:

# Correct:
raise ZeroDivisoionError()

# Wrong:
1 / 0

New in version 0.12.0.

error_template = 'Found explicit zero division'
code = 344
class MeaninglessNumberOperationViolation(node, text=None)[source]

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to use meaningless math opeartions with 0 and 1.

Reasoning:

Adding and substracting zero does not change the value. There’s no need to do that. Multipling by zero is also redundunt: it can be replaced with explicit 0 assign. Multiplying and dividing by 1 is also meaningless.

Solution:

Remove useless zero operaionts.

Example:

# Correct:
number = 1
zero = 0
one = 1

# Wrong:
number = 1 + 0 * 1
zero = some * 0 / 1
one = some ** 0 ** 1

New in version 0.12.0.

error_template = 'Found meaningless number operation'
code = 345
class OperationSignNegationViolation(node, text=None)[source]

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to have double minus operations.

Reasoning:

Having two operations is harder than having just one. Two negations are harder than one positive expression. Two negations equal to one positive expression. Positive and negative equal to one negative.

Solution:

Replace double minus operation to a single one with plus. Replace ‘plus-minus’ operation to a single one with minus.

Example:

# Correct:
number = 3 + 1
number += 6
number -= 2

# Wrong:
number = 3 - -1
number -= -6
number += -2

New in version 0.12.0.

error_template = 'Found wrong operation sign'
code = 346