Bug, variables from blacklisted names looks like _{BLACKLISTED NAMES} are ignored (#19)

Closes #15

Author: barsovichok

.gitignore

@@ -1,6 +1,7 @@
 #### joe made this: http://goel.io/joe
 #### python ####
 # Byte-compiled / optimized / DLL files
+.pytest_cache
 __pycache__/
 *.py[cod]
 *$py.class

tests/fixtures/wrong_variable.py

@@ -0,0 +1,55 @@
+# -*- coding: utf-8 -*-
+
+"""
+This file contains all broken variable names.
+"""
+_data = 1
+_result = 1
+__author__ = 'John Doe'  # error here
+
+x = 1  # error here
+
+
+def fixture():
+    __author__ = 'John Doe'  # no error, because not module metadata
+
+
+def check_function_args(data, t, *a, **vals):  # 4 errors here
+    result = data + t  # error here for `result`
+    return result
+
+
+with open('missing.txt') as f:  # error here
+    contents = f.read()  # error here
+    print(contents)
+
+
+for item in range(1, 3):  # error here
+    continue
+
+
+for _ in range(1, 3):  # should not raise error here
+    continue
+
+
+try:
+    1 / 0
+except ZeroDivisionError as e:  # TODO: error here
+    pass
+
+
+class Fixture(object):
+    data = 'data'  # error here
+    result: int  # error here
+
+    def __init__(self, value):  # error here
+        self.var = value  # error here only for `var`, not for `value`
+        self.x = value  # error here only for `x`, not for `value`
+
+
+val = Fixture()  # error here
+print(val.var)  # no error here
+print(val.x)  # no error here
+
+if val:
+    __author__ = 'John'  # no error here since it's a rare use of module meta

tests/test_checkers/test_wrong_variable.py

@@ -0,0 +1,22 @@
+# -*- coding: utf-8 -*-
+
+import subprocess
+
+
+def test_wrong_variables_in_fixture(absolute_path):
+    """End-to-End test to check variable rules."""
+    filename = absolute_path('fixtures', 'wrong_variable.py')
+    process = subprocess.Popen(
+        ['flake8', filename],
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
+    )
+    stdout, _ = process.communicate()
+
+    assert stdout.count(b'WPS120') == 8
+    assert stdout.count(b'WPS121') == 3
+    assert stdout.count(b'WPS122') == 3
+    assert stdout.count(b'WPS123') == 2
+    assert stdout.count(b'WPS124') == 1
+    assert stdout.count(b'WPS125') == 1
+    assert stdout.count(b'WPS126') == 1

tests/test_visitors/test_wrong_name/test_variable_names.py

@@ -15,6 +15,22 @@
 {0} = 'test'
 """
 
+underscore_variable_test1 = """
+_{0} = 'test'
+"""
+
+underscore_variable_test2 = """
+{0}_ = 'test'
+"""
+
+underscore_variable_test3 = """
+__{0} = 'test'
+"""
+
+underscore_variable_test4 = """
+{0}__ = 'test'
+"""
+
 for_variable_test = """
 for {0} in []:
     print()
@@ -39,6 +55,10 @@
     for_variable_test,
     with_variable_test,
     exception_test,
+    underscore_variable_test1,
+    underscore_variable_test2,
+    underscore_variable_test3,
+    underscore_variable_test4,
 ])
 def test_wrong_variable_names(
     assert_errors, parse_ast_tree, bad_name, code,
@@ -77,6 +97,10 @@ def test_too_short_variable_names(
     for_variable_test,
     with_variable_test,
     exception_test,
+    underscore_variable_test1,
+    underscore_variable_test2,
+    underscore_variable_test3,
+    underscore_variable_test4,
 ])
 def test_correct_variable_name(
     assert_errors, parse_ast_tree, code, correct_name,

wemake_python_styleguide/helpers/variables.py

@@ -9,12 +9,22 @@ def is_wrong_variable_name(name: str, to_check: Iterable[str]) -> bool:
 
     >>> is_wrong_variable_name('wrong', ['wrong'])
     True
-
     >>> is_wrong_variable_name('correct', ['wrong'])
     False
-
+    >>> is_wrong_variable_name('__wrong', ['wrong'])
+    True
     """
-    return name in to_check
+    for name_to_check in to_check:
+        choices_to_check = [
+            name_to_check,
+            '_{0}'.format(name_to_check),
+            '{0}_'.format(name_to_check),
+            '__{0}'.format(name_to_check),
+            '{0}__'.format(name_to_check),
+        ]
+        if name in choices_to_check:
+            return True
+    return False
 
 
 def is_too_short_variable_name(