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.
BadNumberSuffixViolation Forbids to use capital X, O, B, and E in numbers.
ComparisonOrderViolation Forbids comparision where argument doesn’t come first.
MultipleInComparisonViolation Forbids comparision where multiple in checks.
RedundantComparisonViolation Forbids to have comparisons between the same variable.
MissingSpaceBetweenKeywordAndParenViolation Forbid opening parenthesis from following keyword without space in between.
WrongConditionalViolation Forbids using if statements that use invalid conditionals.
ObjectInBaseClassesListViolation Forbid extra object in parent classes list.

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.

Note

Returns Z300 as error code

error_template = 'Found local folder import'

Error message shown to the user.

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.

Note

Returns Z301 as error code

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

Error message shown to the user.

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.

Note

Returns Z302 as error code

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

Error message shown to the user.

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 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.

Note

Returns Z303 as error code

error_template = 'Found underscored number: {0}'

Error message shown to the user.

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.

Note

Returns Z304 as error code

error_template = 'Found partial float: {0}'

Error message shown to the user.

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

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to use f strings.

Reasoning:
f strings looses 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.

Note

Returns Z305 as error code

error_template = 'Found `f` string'

Error message shown to the user.

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.

Note

Returns Z306 as error code

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

Error message shown to the user.

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.

Note

Returns Z307 as error code

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

Error message shown to the user.

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

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.

Note

Returns Z308 as error code

error_template = 'Found constant comparison'

Error message shown to the user.

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.

Note

Returns Z310 as error code

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

Error message shown to the user.

class ComparisonOrderViolation(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 a 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.

Note

Returns Z309 as error code

error_template = 'Found reversed comparison order'

Error message shown to the user.

class MultipleInComparisonViolation(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 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.

Note

Returns Z311 as error code

error_template = 'Found multiple `in` comparisons'

Error message shown to the user.

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

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.

Note

Returns Z312 as error code

error_template = 'Found comparison between same variable'

Error message shown to the user.

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

Bases: wemake_python_styleguide.violations.base.TokenizeViolation

Forbid opening parenthesis from following keyword without space in between.

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.

Note

Returns Z313 as error code

error_template = 'Found parens right after a keyword'

Error message shown to the user.

class WrongConditionalViolation(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.

Note

Returns Z314 as error code

error_template = 'Conditional always evaluates to same result'

Error message shown to the user.

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

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbid 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 an other 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.

Note

Returns Z315 as error code

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

Error message shown to the user