B001: do not use bare except

README.rst

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+==============
+flake8-bugbear
+==============
+
+A plugin for flake8 finding likely bugs and design problems in your
+program.  Contains warnings that don't belong in pyflakes and pep8::
+
+    bug·bear  (bŭg′bâr′)
+    n.
+    1. A cause of fear, anxiety, or irritation: *Overcrowding is often
+       a bugbear for train commuters.*
+    2. A difficult or persistent problem: *"One of the major bugbears of
+       traditional AI is the difficulty of programming computers to
+       recognize that different but similar objects are instances of the
+       same type of thing" (Jack Copeland).*
+    3. A fearsome imaginary creature, especially one evoked to frighten
+       children.
+
+List of warnings
+----------------
+
+B001
+~~~~
+
+Do not use bare ``except:``, it also catches unexpected events " "like
+memory errors, interrupts, system exit, and so on.  Prefer ``except
+Exception:``.  If you're sure what you're doing, be explicit and write
+``except BaseException:``.
+
+Tests
+-----
+
+Just run::
+
+    python setup.py test
+
+
+License
+-------
+
+MIT
+
+
+Change Log
+----------
+
+16.4.0
+~~~~~~
+
+* first published version
+
+* date-versioned
+
+
+Authors
+-------
+
+Glued together by `Łukasz Langa <mailto:[email protected]>`_.

bugbear.py

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+import ast
+from collections import namedtuple
+from functools import partial
+
+import attr
+import pep8
+
+
+__version__ = '16.4.0'
+
+
+@attr.s
+class BugBearChecker(object):
+    name = 'flake8-bugbear'
+    version = __version__
+
+    tree = attr.ib(default=None)
+    filename = attr.ib(default='(none)')
+    builtins = attr.ib(default=None)
+    lines = attr.ib(default=None)
+    visitor = attr.ib(default=attr.Factory(lambda: BugBearVisitor))
+
+    def run(self):
+        if not self.tree or not self.lines:
+            self.load_file()
+        visitor = self.visitor(
+            filename=self.filename,
+            lines=self.lines,
+        )
+        visitor.visit(self.tree)
+        for e in visitor.errors:
+            if pep8.noqa(self.lines[e.lineno - 1]):
+                continue
+
+            yield e
+
+    def load_file(self):
+        """Loads the file in a way that auto-detects source encoding and deals
+        with broken terminal encodings for stdin.
+
+        Stolen from flake8_import_order because it's good.
+        """
+
+        if self.filename in ("stdin", "-", None):
+            self.filename = "stdin"
+            self.lines = pep8.stdin_get_value().splitlines(True)
+        else:
+            self.lines = pep8.readlines(self.filename)
+
+        if not self.tree:
+            self.tree = ast.parse("".join(self.lines))
+
+
+@attr.s
+class BugBearVisitor(ast.NodeVisitor):
+    filename = attr.ib()
+    lines = attr.ib()
+    node_stack = attr.ib(default=attr.Factory(list))
+    errors = attr.ib(default=attr.Factory(list))
+
+    if False:
+        # Useful for tracing what the hell is going on.
+
+        def __getattr__(self, name):
+            print(name)
+            return self.__getattribute__(name)
+
+    def visit(self, node):
+        self.node_stack.append(node)
+        super().visit(node)
+        self.node_stack.pop()
+
+    def visit_ExceptHandler(self, node):
+        if node.type is None:
+            self.errors.append(
+                B001(node.lineno, node.col_offset)
+            )
+
+
+error = namedtuple('error', 'lineno col message type')
+B001 = partial(
+    error,
+    message="B001: Do not use bare `except:`, it also catches unexpected "
+            "events like memory errors, interrupts, system exit, and so on.  "
+            "Prefer `except Exception:`.  If you're sure what you're doing, "
+            "be explicit and write `except BaseException:`.",
+    type=BugBearChecker,
+)
+

setup.py

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+# Copyright (C) 2016 Łukasz Langa
+
+import ast
+import os
+import re
+from setuptools import setup
+
+
+current_dir = os.path.abspath(os.path.dirname(__file__))
+ld_file = open(os.path.join(current_dir, 'README.rst'))
+try:
+    long_description = ld_file.read()
+finally:
+    ld_file.close()
+
+
+_version_re = re.compile(r'__version__\s+=\s+(?P<version>.*)')
+
+
+with open('bugbear.py', 'rb') as f:
+    version = _version_re.search(f.read().decode('utf-8')).group('version')
+    version = str(ast.literal_eval(version))
+
+
+setup(
+    name='flake8-bugbear',
+    version=version,
+    description="A plugin for flake8 finding likely bugs and design problems "
+                "in your program. Contains warnings that don't belong in "
+                "pyflakes and pep8.",
+    long_description=long_description,
+    keywords='flake8 bugbear bugs pyflakes pylint linter qa',
+    author='Łukasz Langa',
+    author_email='[email protected]',
+    url='https://github.com/ambv/flake8-bugbear',
+    license='MIT',
+    py_modules=['bugbear'],
+    zip_safe=False,
+    install_requires = ['flake8', 'attrs'],
+    test_suite='tests.test_bugbear',
+    classifiers=[
+        'Development Status :: 3 - Alpha',
+        'Environment :: Console',
+        'Intended Audience :: Developers',
+        'License :: OSI Approved :: MIT License',
+        'Operating System :: OS Independent',
+        'Programming Language :: Python',
+        'Programming Language :: Python :: 3 :: Only',
+        'Topic :: Software Development :: Libraries :: Python Modules',
+        'Topic :: Software Development :: Quality Assurance',
+    ],
+    entry_points={
+        'flake8.extension': [
+            'B00 = bugbear:BugBearChecker',
+        ],
+    },
+)

tests/b001.py

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+"""
+Should emit:
+B001 - on lines 8 and 40
+"""
+
+try:
+    import something
+except:
+    # should be except ImportError:
+    import something_else as something
+
+try:
+    pass
+except ValueError:
+    # no warning here, all good
+    pass
+
+try:
+    pass
+except (KeyError, IndexError):
+    # no warning here, all good
+    pass
+
+try:
+    pass
+except BaseException as be:
+    # no warning here, all good
+    pass
+
+try:
+    pass
+except BaseException:
+    # no warning here, all good
+    pass
+
+
+def func(**kwargs):
+    try:
+        is_debug = kwargs['debug']
+    except:
+        # should be except KeyError:
+        return
+
+    results = something.call(debug=is_debug)
+    try:
+        results['ok']
+    except:  # noqa
+        # warning silenced
+        return

tests/test_bugbear.py

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+from pathlib import Path
+import unittest
+
+from bugbear import BugBearChecker, B001
+
+
+class BugbearTestCase(unittest.TestCase):
+    maxDiff = None
+
+    def test_b001(self):
+        filename = Path(__file__).absolute().parent / 'b001.py'
+        bbc = BugBearChecker(filename=str(filename))
+        errors = list(bbc.run())
+        self.assertEqual(
+            errors,
+            [B001(8, 0), B001(40, 4)],
+        )
+
+
+if __name__ == '__main__':
+    unittest.main()