Add checks to maintain a consistent Python code style and prevent bugs (

pybind#515)

A flake8 configuration is included in setup.cfg and the checks are
executed automatically on Travis:

* Ensures a consistent PEP8 code style
* Does basic linting to prevent possible bugs

.travis.yml

@@ -38,11 +38,12 @@ matrix:
   # Documentation build:
   - os: linux
     language: docs
-    env: DOCS STYLE
-    install: pip install sphinx sphinx_rtd_theme
+    env: DOCS STYLE LINT
+    install: pip install sphinx sphinx_rtd_theme flake8 pep8-naming
     script:
     - make -C docs html SPHINX_OPTIONS=-W
     - tools/check-style.sh
+    - flake8
 cache:
   directories:
   - $HOME/.cache/pip

pybind11/__init__.py

@@ -1,4 +1,4 @@
-from ._version import version_info, __version__
+from ._version import version_info, __version__  # noqa: F401 imported but unused
 
 
 def get_include(*args, **kwargs):

setup.cfg

@@ -1,2 +1,11 @@
 [bdist_wheel]
 universal=1
+
+[flake8]
+show_source = True
+exclude = .git, __pycache__, build, dist, docs, tools, venv
+ignore =
+    # line too long
+    E501,
+    # required for pretty matrix formating: multiple spaces after `,` and `[`
+    E201, E241

tests/conftest.py

@@ -8,13 +8,12 @@
 import textwrap
 import difflib
 import re
-import os
 import sys
 import contextlib
 
 _unicode_marker = re.compile(r'u(\'[^\']*\')')
-_long_marker    = re.compile(r'([0-9])L')
-_hexadecimal    = re.compile(r'0x[0-9a-fA-F]+')
+_long_marker = re.compile(r'([0-9])L')
+_hexadecimal = re.compile(r'0x[0-9a-fA-F]+')
 
 
 def _strip_and_dedent(s):
@@ -218,7 +217,7 @@ def _test_import_pybind11():
     """
     # noinspection PyBroadException
     try:
-        import pybind11_tests
+        import pybind11_tests  # noqa: F401 imported but unused
     except Exception as e:
         print("Failed to import pybind11_tests from pytest:")
         print("  {}: {}".format(type(e).__name__, e))

tests/test_alias_initialization.py

@@ -1,12 +1,11 @@
-import pytest
 import gc
 
-def test_alias_delay_initialization(capture, msg):
 
-    # A only initializes its trampoline class when we inherit from it; if we
-    # just create and use an A instance directly, the trampoline initialization
-    # is bypassed and we only initialize an A() instead (for performance
-    # reasons)
+def test_alias_delay_initialization1(capture):
+    """A only initializes its trampoline class when we inherit from it; if we just
+    create and use an A instance directly, the trampoline initialization is bypassed
+    and we only initialize an A() instead (for performance reasons).
+    """
     from pybind11_tests import A, call_f
 
     class B(A):
@@ -37,14 +36,14 @@ def f(self):
         PyA.~PyA()
     """
 
-def test_alias_delay_initialization(capture, msg):
-    from pybind11_tests import A2, call_f
 
-    # A2, unlike the above, is configured to always initialize the alias; while
-    # the extra initialization and extra class layer has small virtual dispatch
-    # performance penalty, it also allows us to do more things with the
-    # trampoline class such as defining local variables and performing
-    # construction/destruction.
+def test_alias_delay_initialization2(capture):
+    """A2, unlike the above, is configured to always initialize the alias; while
+    the extra initialization and extra class layer has small virtual dispatch
+    performance penalty, it also allows us to do more things with the trampoline
+    class such as defining local variables and performing construction/destruction.
+    """
+    from pybind11_tests import A2, call_f
 
     class B2(A2):
         def __init__(self):

tests/test_chrono.py

@@ -47,7 +47,7 @@ def test_chrono_duration_roundtrip():
     from pybind11_tests import test_chrono3
     import datetime
 
-    # Get the difference betwen two times (a timedelta)
+    # Get the difference between two times (a timedelta)
     date1 = datetime.datetime.today()
     date2 = datetime.datetime.today()
     diff = date2 - date1

tests/test_class_args.py

@@ -1,5 +1,4 @@
 
-import pytest
 
 def test_class_args():
     # There's basically nothing to test here; just make sure the code compiled and declared its definition

tests/test_copy_move_policies.py

@@ -13,5 +13,3 @@ def test_lacking_move_ctor():
     with pytest.raises(RuntimeError) as excinfo:
         lacking_move_ctor.get_one()
     assert "the object is neither movable nor copyable!" in str(excinfo.value)
-
-

tests/test_docstring_options.py

@@ -1,6 +1,6 @@
-from pybind11_tests import ConstructorStats
 
-def test_docstring_options(capture):
+
+def test_docstring_options():
     from pybind11_tests import (test_function1, test_function2, test_function3,
                                 test_function4, test_function5, test_function6,
                                 test_function7, DocstringTestFoo)

tests/test_enum.py

@@ -30,10 +30,6 @@ def test_unscoped_enum():
     assert not (UnscopedEnum.ETwo < UnscopedEnum.EOne)
     assert not (2 < UnscopedEnum.EOne)
 
-def test_scoped_enum():
-    from pybind11_tests import ScopedEnum, test_scoped_enum
-
-    assert test_scoped_enum(ScopedEnum.Three) == "ScopedEnum::Three"
 
 def test_scoped_enum():
     from pybind11_tests import ScopedEnum, test_scoped_enum
@@ -56,6 +52,7 @@ def test_scoped_enum():
     assert ScopedEnum.Two >= ScopedEnum.Two
     assert ScopedEnum.Three >= ScopedEnum.Two
 
+
 def test_implicit_conversion():
     from pybind11_tests import ClassWithUnscopedEnum
 
@@ -87,6 +84,7 @@ def test_implicit_conversion():
     # Hashing test
     assert str(x) == "{EMode.EFirstMode: 3, EMode.ESecondMode: 4}"
 
+
 def test_binary_operators():
     from pybind11_tests import Flags
 
@@ -108,4 +106,3 @@ def test_binary_operators():
     state2 = ~state
     assert state2 == -7
     assert int(state ^ state2) == -1
-

tests/test_eval_call.py

@@ -1,4 +1,4 @@
 # This file is called from 'test_eval.py'
 
 if 'call_test2' in locals():
-    call_test2(y)
+    call_test2(y)  # noqa: F821 undefined name

tests/test_exceptions.py

@@ -69,6 +69,6 @@ def test_custom(msg):
     with pytest.raises(MyException5) as excinfo:
         try:
             throws5()
-        except MyException5_1 as e:
+        except MyException5_1:
             raise RuntimeError("Exception error: caught child from parent")
     assert msg(excinfo.value) == "this is a helper-defined translated exception"

tests/test_issues.py

@@ -83,7 +83,6 @@ def test_no_id(msg):
     assert expect_float(12) == 12
 
 
-
 def test_str_issue(msg):
     """Issue #283: __str__ called on uninitialized instance when constructor arguments invalid"""
     from pybind11_tests.issues import StrIssue
@@ -153,8 +152,8 @@ def test_override_ref():
     o = OverrideTest("asdf")
 
     # Not allowed (see associated .cpp comment)
-    #i = o.str_ref()
-    #assert o.str_ref() == "asdf"
+    # i = o.str_ref()
+    # assert o.str_ref() == "asdf"
     assert o.str_value() == "asdf"
 
     assert o.A_value().value == "hi"
@@ -167,15 +166,17 @@ def test_override_ref():
 def test_operators_notimplemented(capture):
     from pybind11_tests.issues import OpTest1, OpTest2
     with capture:
-        C1, C2 = OpTest1(), OpTest2()
-        C1 + C1
-        C2 + C2
-        C2 + C1
-        C1 + C2
-    assert capture == """Add OpTest1 with OpTest1
-Add OpTest2 with OpTest2
-Add OpTest2 with OpTest1
-Add OpTest2 with OpTest1"""
+        c1, c2 = OpTest1(), OpTest2()
+        c1 + c1
+        c2 + c2
+        c2 + c1
+        c1 + c2
+    assert capture == """
+        Add OpTest1 with OpTest1
+        Add OpTest2 with OpTest2
+        Add OpTest2 with OpTest1
+        Add OpTest2 with OpTest1
+    """
 
 
 def test_iterator_rvpolicy():
@@ -185,7 +186,7 @@ def test_iterator_rvpolicy():
 
     assert list(make_iterator_1()) == [1, 2, 3]
     assert list(make_iterator_2()) == [1, 2, 3]
-    assert(type(make_iterator_1()) != type(make_iterator_2()))
+    assert not isinstance(make_iterator_1(), type(make_iterator_2()))
 
 
 def test_dupe_assignment():
@@ -234,9 +235,9 @@ def test_complex_cast(capture):
         test_complex(2j)
 
     assert capture == """
-1.0
-(0.0, 2.0)
-"""
+        1.0
+        (0.0, 2.0)
+    """
 
 
 def test_inheritance_override_def_static():

tests/test_keep_alive.py

@@ -95,4 +95,3 @@ def test_return_none(capture):
         del p
         gc.collect()
     assert capture == "Releasing parent."
-

tests/test_methods_and_attributes.py

@@ -113,7 +113,8 @@ def test_property_return_value_policies(access):
 
 def test_property_rvalue_policy():
     """When returning an rvalue, the return value policy is automatically changed from
-       `reference(_internal)` to `move`. The following would not work otherwise."""
+    `reference(_internal)` to `move`. The following would not work otherwise.
+    """
     from pybind11_tests import TestPropRVP
 
     instance = TestPropRVP()

tests/test_multiple_inheritance.py

@@ -1,7 +1,6 @@
-import pytest
 
 
-def test_multiple_inheritance_cpp(msg):
+def test_multiple_inheritance_cpp():
     from pybind11_tests import MIType
 
     mt = MIType(3, 4)
@@ -10,7 +9,7 @@ def test_multiple_inheritance_cpp(msg):
     assert mt.bar() == 4
 
 
-def test_multiple_inheritance_mix1(msg):
+def test_multiple_inheritance_mix1():
     from pybind11_tests import Base2
 
     class Base1:
@@ -31,7 +30,7 @@ def __init__(self, i, j):
     assert mt.bar() == 4
 
 
-def test_multiple_inheritance_mix2(msg):
+def test_multiple_inheritance_mix2():
     from pybind11_tests import Base1
 
     class Base2:
@@ -52,7 +51,7 @@ def __init__(self, i, j):
     assert mt.bar() == 4
 
 
-def test_multiple_inheritance_virtbase(msg):
+def test_multiple_inheritance_virtbase():
     from pybind11_tests import Base12a, bar_base2a, bar_base2a_sharedptr
 
     class MITypePy(Base12a):

tests/test_numpy_array.py

@@ -144,10 +144,10 @@ def test_bounds_check(arr):
              mutate_data, mutate_data_t, at_t, mutate_at_t)
     for func in funcs:
         with pytest.raises(IndexError) as excinfo:
-            index_at(arr, 2, 0)
+            func(arr, 2, 0)
         assert str(excinfo.value) == 'index 2 is out of bounds for axis 0 with size 2'
         with pytest.raises(IndexError) as excinfo:
-            index_at(arr, 0, 4)
+            func(arr, 0, 4)
         assert str(excinfo.value) == 'index 4 is out of bounds for axis 1 with size 3'
 
 
@@ -166,50 +166,49 @@ def test_make_c_f_array():
 def test_wrap():
     from pybind11_tests.array import wrap
 
-    def assert_references(A, B):
-        assert A is not B
-        assert A.__array_interface__['data'][0] == \
-               B.__array_interface__['data'][0]
-        assert A.shape == B.shape
-        assert A.strides == B.strides
-        assert A.flags.c_contiguous == B.flags.c_contiguous
-        assert A.flags.f_contiguous == B.flags.f_contiguous
-        assert A.flags.writeable == B.flags.writeable
-        assert A.flags.aligned == B.flags.aligned
-        assert A.flags.updateifcopy == B.flags.updateifcopy
-        assert np.all(A == B)
-        assert not B.flags.owndata
-        assert B.base is A
-        if A.flags.writeable and A.ndim == 2:
-            A[0, 0] = 1234
-            assert B[0, 0] == 1234
-
-    A1 = np.array([1, 2], dtype=np.int16)
-    assert A1.flags.owndata and A1.base is None
-    A2 = wrap(A1)
-    assert_references(A1, A2)
-
-    A1 = np.array([[1, 2], [3, 4]], dtype=np.float32, order='F')
-    assert A1.flags.owndata and A1.base is None
-    A2 = wrap(A1)
-    assert_references(A1, A2)
-
-    A1 = np.array([[1, 2], [3, 4]], dtype=np.float32, order='C')
-    A1.flags.writeable = False
-    A2 = wrap(A1)
-    assert_references(A1, A2)
-
-    A1 = np.random.random((4, 4, 4))
-    A2 = wrap(A1)
-    assert_references(A1, A2)
-
-    A1 = A1.transpose()
-    A2 = wrap(A1)
-    assert_references(A1, A2)
-
-    A1 = A1.diagonal()
-    A2 = wrap(A1)
-    assert_references(A1, A2)
+    def assert_references(a, b):
+        assert a is not b
+        assert a.__array_interface__['data'][0] == b.__array_interface__['data'][0]
+        assert a.shape == b.shape
+        assert a.strides == b.strides
+        assert a.flags.c_contiguous == b.flags.c_contiguous
+        assert a.flags.f_contiguous == b.flags.f_contiguous
+        assert a.flags.writeable == b.flags.writeable
+        assert a.flags.aligned == b.flags.aligned
+        assert a.flags.updateifcopy == b.flags.updateifcopy
+        assert np.all(a == b)
+        assert not b.flags.owndata
+        assert b.base is a
+        if a.flags.writeable and a.ndim == 2:
+            a[0, 0] = 1234
+            assert b[0, 0] == 1234
+
+    a1 = np.array([1, 2], dtype=np.int16)
+    assert a1.flags.owndata and a1.base is None
+    a2 = wrap(a1)
+    assert_references(a1, a2)
+
+    a1 = np.array([[1, 2], [3, 4]], dtype=np.float32, order='F')
+    assert a1.flags.owndata and a1.base is None
+    a2 = wrap(a1)
+    assert_references(a1, a2)
+
+    a1 = np.array([[1, 2], [3, 4]], dtype=np.float32, order='C')
+    a1.flags.writeable = False
+    a2 = wrap(a1)
+    assert_references(a1, a2)
+
+    a1 = np.random.random((4, 4, 4))
+    a2 = wrap(a1)
+    assert_references(a1, a2)
+
+    a1 = a1.transpose()
+    a2 = wrap(a1)
+    assert_references(a1, a2)
+
+    a1 = a1.diagonal()
+    a2 = wrap(a1)
+    assert_references(a1, a2)
 
 
 @pytest.requires_numpy