bears/python: Add PyFlakesBear

Closes coala#825

bears/python/PyFlakesBear.py

@@ -0,0 +1,29 @@
+from coalib.bearlib.abstractions.Linter import linter
+from coalib.bears.requirements.PipRequirement import PipRequirement
+from coalib.results.RESULT_SEVERITY import RESULT_SEVERITY
+
+
+@linter(executable='pyflakes',
+        output_format='regex',
+        output_regex=r'(?P<filename>.*):(?P<line>\d+):'
+                     r'(?P<severity>)\s(?P<message>.*)',
+        severity_map={
+            '': RESULT_SEVERITY.INFO
+        })
+class PyFlakesBear:
+    """
+    Checks Python files for errors using ``pyflakes``.
+
+    See https://github.com/PyCQA/pyflakes for more info.
+    """
+    LANGUAGES = {"Python", "Python 3"}
+    REQUIREMENTS = {PipRequirement('pyflakes', '1.2.*')}
+    AUTHORS = {'The coala developers'}
+    AUTHORS_EMAILS = {'[email protected]'}
+    LICENSE = 'AGPL-3.0'
+    ASCIINEMA_URL = 'https://asciinema.org/a/92503'
+    CAN_DETECT = {'Unused imports', 'Undefined Element'}
+
+    @staticmethod
+    def create_arguments(filename, file, config_file):
+        return filename,

requirements.txt

@@ -28,6 +28,6 @@ pyyaml==3.*
 vulture==0.10.*
 bandit==1.1.*
 nbformat>=4.*
-pyflakes==1.2.*  # Although we don't need this directly, solves a dep conflict
+pyflakes==1.2.*
 scspell3k==2.*
 mypy-lang==0.4.*

tests/python/PyFlakesBearTest.py

@@ -0,0 +1,15 @@
+from bears.python.PyFlakesBear import PyFlakesBear
+from tests.LocalBearTestHelper import verify_local_bear
+
+good_file = """
+print("Hi")
+"""
+
+bad_file = """
+import os
+print("Hi")
+"""
+
+PyFlakesBear = verify_local_bear(PyFlakesBear,
+                                 valid_files=(good_file,),
+                                 invalid_files=(bad_file,))