# Copyright (c) 2003-2013 LOGILAB S.A. (Paris, FRANCE).
# http://www.logilab.fr/ -- mailto:contact@logilab.fr
# This program is free software; you can redistribute it and/or modify it under
# the terms of the GNU General Public License as published by the Free Software
# Foundation; either version 2 of the License, or (at your option) any later
# version.
#
# This program is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
# FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License along with
# this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
"""exceptions handling (raising, catching, exceptions classes) checker
"""
import sys
import astroid
from astroid import YES, Instance, unpack_infer, List, Tuple
from logilab.common.compat import builtins
from pylint.checkers import BaseChecker
from pylint.checkers.utils import (
is_empty,
is_raising,
check_messages,
inherit_from_std_ex,
EXCEPTIONS_MODULE,
has_known_bases,
safe_infer)
from pylint.interfaces import IAstroidChecker, INFERENCE, INFERENCE_FAILURE
def _annotated_unpack_infer(stmt, context=None):
"""
Recursively generate nodes inferred by the given statement.
If the inferred value is a list or a tuple, recurse on the elements.
Returns an iterator which yields tuples in the format
('original node', 'infered node').
"""
if isinstance(stmt, (List, Tuple)):
for elt in stmt.elts:
inferred = safe_infer(elt)
if inferred and inferred is not YES:
yield elt, inferred
return
for infered in stmt.infer(context):
if infered is YES:
continue
yield stmt, infered
PY3K = sys.version_info >= (3, 0)
OVERGENERAL_EXCEPTIONS = ('Exception',)
BUILTINS_NAME = builtins.__name__
MSGS = {
'E0701': ('Bad except clauses order (%s)',
'bad-except-order',
'Used when except clauses are not in the correct order (from the '
'more specific to the more generic). If you don\'t fix the order, '
'some exceptions may not be catched by the most specific handler.'),
'E0702': ('Raising %s while only classes or instances are allowed',
'raising-bad-type',
'Used when something which is neither a class, an instance or a \
string is raised (i.e. a `TypeError` will be raised).'),
'E0703': ('Exception context set to something which is not an '
'exception, nor None',
'bad-exception-context',
'Used when using the syntax "raise ... from ...", '
'where the exception context is not an exception, '
'nor None.',
{'minversion': (3, 0)}),
'E0710': ('Raising a new style class which doesn\'t inherit from BaseException',
'raising-non-exception',
'Used when a new style class which doesn\'t inherit from \
BaseException is raised.'),
'E0711': ('NotImplemented raised - should raise NotImplementedError',
'notimplemented-raised',
'Used when NotImplemented is raised instead of \
NotImplementedError'),
'E0712': ('Catching an exception which doesn\'t inherit from BaseException: %s',
'catching-non-exception',
'Used when a class which doesn\'t inherit from \
BaseException is used as an exception in an except clause.'),
'W0702': ('No exception type(s) specified',
'bare-except',
'Used when an except clause doesn\'t specify exceptions type to \
catch.'),
'W0703': ('Catching too general exception %s',
'broad-except',
'Used when an except catches a too general exception, \
possibly burying unrelated errors.'),
'W0704': ('Except doesn\'t do anything',
'pointless-except',
'Used when an except clause does nothing but "pass" and there is\
no "else" clause.'),
'W0710': ('Exception doesn\'t inherit from standard "Exception" class',
'nonstandard-exception',
'Used when a custom exception class is raised but doesn\'t \
inherit from the builtin "Exception" class.',
{'maxversion': (3, 0)}),
'W0711': ('Exception to catch is the result of a binary "%s" operation',
'binary-op-exception',
'Used when the exception to catch is of the form \
"except A or B:". If intending to catch multiple, \
rewrite as "except (A, B):"'),
}
class ExceptionsChecker(BaseChecker):
"""checks for
* excepts without exception filter
* type of raise argument : string, Exceptions, other values
"""
__implements__ = IAstroidChecker
name = 'exceptions'
msgs = MSGS
priority = -4
options = (('overgeneral-exceptions',
{'default' : OVERGENERAL_EXCEPTIONS,
'type' :'csv', 'metavar' : '<comma-separated class names>',
'help' : 'Exceptions that will emit a warning '
'when being caught. Defaults to "%s"' % (
', '.join(OVERGENERAL_EXCEPTIONS),)}
),
)
@check_messages('nonstandard-exception',
'raising-bad-type', 'raising-non-exception',
'notimplemented-raised', 'bad-exception-context')
def visit_raise(self, node):
"""visit raise possibly inferring value"""
# ignore empty raise
if node.exc is None:
return
if PY3K and node.cause:
self._check_bad_exception_context(node)
expr = node.exc
if self._check_raise_value(node, expr):
return
else:
try:
value = next(unpack_infer(expr))
except astroid.InferenceError:
return
self._check_raise_value(node, value)
def _check_bad_exception_context(self, node):
"""Verify that the exception context is properly set.
An exception context can be only `None` or an exception.
"""
cause = safe_infer(node.cause)
if cause in (YES, None):
return
if isinstance(cause, astroid.Const):
if cause.value is not None:
self.add_message('bad-exception-context',
node=node)
elif (not isinstance(cause, astroid.Class) and
not inherit_from_std_ex(cause)):
self.add_message('bad-exception-context',
node=node)
def _check_raise_value(self, node, expr):
"""check for bad values, string exception and class inheritance
"""
value_found = True
if isinstance(expr, astroid.Const):
value = expr.value
if not isinstance(value, str):
# raising-string will be emitted from python3 porting checker.
self.add_message('raising-bad-type', node=node,
args=value.__class__.__name__)
elif ((isinstance(expr, astroid.Name) and
expr.name in ('None', 'True', 'False')) or
isinstance(expr, (astroid.List, astroid.Dict, astroid.Tuple,
astroid.Module, astroid.Function))):
emit = True
if not PY3K and isinstance(expr, astroid.Tuple):
# On Python 2, using the following is not an error:
# raise (ZeroDivisionError, None)
# raise (ZeroDivisionError, )
# What's left to do is to check that the first
# argument is indeed an exception.
# Verifying the other arguments is not
# the scope of this check.
first = expr.elts[0]
inferred = safe_infer(first)
if isinstance(inferred, Instance):
# pylint: disable=protected-access
inferred = inferred._proxied
if (inferred is YES or
isinstance(inferred, astroid.Class)
and inherit_from_std_ex(inferred)):
emit = False
if emit:
self.add_message('raising-bad-type',
node=node,
args=expr.name)
elif ((isinstance(expr, astroid.Name) and expr.name == 'NotImplemented')
or (isinstance(expr, astroid.CallFunc) and
isinstance(expr.func, astroid.Name) and
expr.func.name == 'NotImplemented')):
self.add_message('notimplemented-raised', node=node)
elif isinstance(expr, (Instance, astroid.Class)):
if isinstance(expr, Instance):
# pylint: disable=protected-access
expr = expr._proxied
if (isinstance(expr, astroid.Class) and
not inherit_from_std_ex(expr)):
if expr.newstyle:
self.add_message('raising-non-exception', node=node)
else:
if has_known_bases(expr):
confidence = INFERENCE
else:
confidence = INFERENCE_FAILURE
self.add_message(
'nonstandard-exception', node=node,
confidence=confidence)
else:
value_found = False
else:
value_found = False
return value_found
def _check_catching_non_exception(self, handler, exc, part):
if isinstance(exc, astroid.Tuple):
# Check if it is a tuple of exceptions.
inferred = [safe_infer(elt) for elt in exc.elts]
if any(node is astroid.YES for node in inferred):
# Don't emit if we don't know every component.
return
if all(node and inherit_from_std_ex(node)
for node in inferred):
return
if not isinstance(exc, astroid.Class):
# Don't emit the warning if the infered stmt
# is None, but the exception handler is something else,
# maybe it was redefined.
if (isinstance(exc, astroid.Const) and
exc.value is None):
if ((isinstance(handler.type, astroid.Const) and
handler.type.value is None) or
handler.type.parent_of(exc)):
# If the exception handler catches None or
# the exception component, which is None, is
# defined by the entire exception handler, then
# emit a warning.
self.add_message('catching-non-exception',
node=handler.type,
args=(part.as_string(), ))
else:
self.add_message('catching-non-exception',
node=handler.type,
args=(part.as_string(), ))
return
if (not inherit_from_std_ex(exc) and
exc.root().name != BUILTINS_NAME):
if has_known_bases(exc):
self.add_message('catching-non-exception',
node=handler.type,
args=(exc.name, ))
@check_messages('bare-except', 'broad-except', 'pointless-except',
'binary-op-exception', 'bad-except-order',
'catching-non-exception')
def visit_tryexcept(self, node):
"""check for empty except"""
exceptions_classes = []
nb_handlers = len(node.handlers)
for index, handler in enumerate(node.handlers):
# single except doing nothing but "pass" without else clause
if is_empty(handler.body) and not node.orelse:
self.add_message('pointless-except',
node=handler.type or handler.body[0])
if handler.type is None:
if not is_raising(handler.body):
self.add_message('bare-except', node=handler)
# check if a "except:" is followed by some other
# except
if index < (nb_handlers - 1):
msg = 'empty except clause should always appear last'
self.add_message('bad-except-order', node=node, args=msg)
elif isinstance(handler.type, astroid.BoolOp):
self.add_message('binary-op-exception',
node=handler, args=handler.type.op)
else:
try:
excs = list(_annotated_unpack_infer(handler.type))
except astroid.InferenceError:
continue
for part, exc in excs:
if exc is YES:
continue
if (isinstance(exc, astroid.Instance)
and inherit_from_std_ex(exc)):
# pylint: disable=protected-access
exc = exc._proxied
self._check_catching_non_exception(handler, exc, part)
if not isinstance(exc, astroid.Class):
continue
exc_ancestors = [anc for anc in exc.ancestors()
if isinstance(anc, astroid.Class)]
for previous_exc in exceptions_classes:
if previous_exc in exc_ancestors:
msg = '%s is an ancestor class of %s' % (
previous_exc.name, exc.name)
self.add_message('bad-except-order',
node=handler.type, args=msg)
if (exc.name in self.config.overgeneral_exceptions
and exc.root().name == EXCEPTIONS_MODULE
and not is_raising(handler.body)):
self.add_message('broad-except',
args=exc.name, node=handler.type)
exceptions_classes += [exc for _, exc in excs]
def register(linter):
"""required method to auto register this checker"""
linter.register_checker(ExceptionsChecker(linter))