third_party.pylibs.pylint.src/pylint/checkers/stdlib.py

# Copyright 2012 Google Inc.
#
# 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.
"""Checkers for various standard library functions."""

import six
import sys

import astroid
from astroid.bases import Instance
from astroid import helpers

from pylint.interfaces import IAstroidChecker
from pylint.checkers import BaseChecker
from pylint.checkers import utils


TYPECHECK_COMPARISON_OPERATORS = frozenset(('is', 'is not', '==', '!=', 'in', 'not in'))
LITERAL_NODE_TYPES = (astroid.Const, astroid.Dict, astroid.List, astroid.Set)

if sys.version_info >= (3, 0):
    OPEN_MODULE = '_io'
    TYPE_QNAME = 'builtins.type'
else:
    OPEN_MODULE = '__builtin__'
    TYPE_QNAME = '__builtin__.type'


def _check_mode_str(mode):
    # check type
    if not isinstance(mode, six.string_types):
        return False
    # check syntax
    modes = set(mode)
    _mode = "rwatb+U"
    creating = False
    if six.PY3:
        _mode += "x"
        creating = "x" in modes
    if modes - set(_mode) or len(mode) > len(modes):
        return False
    # check logic
    reading = "r" in modes
    writing = "w" in modes
    appending = "a" in modes
    text = "t" in modes
    binary = "b" in modes
    if "U" in modes:
        if writing or appending or creating and six.PY3:
            return False
        reading = True
        if not six.PY3:
            binary = True
    if text and binary:
        return False
    total = reading + writing + appending + (creating if six.PY3 else 0)
    if total > 1:
        return False
    if not (reading or writing or appending or creating and six.PY3):
        return False
    # other 2.x constraints
    if not six.PY3:
        if "U" in mode:
            mode = mode.replace("U", "")
            if "r" not in mode:
                mode = "r" + mode
        return mode[0] in ("r", "w", "a", "U")
    return True


def _is_one_arg_pos_call(call):
    """Is this a call with exactly 1 argument,
    where that argument is positional?
    """
    return (isinstance(call, astroid.CallFunc)
            and len(call.args) == 1 and not call.keywords)


class StdlibChecker(BaseChecker):
    __implements__ = (IAstroidChecker,)
    name = 'stdlib'

    msgs = {
        'W1501': ('"%s" is not a valid mode for open.',
                  'bad-open-mode',
                  'Python supports: r, w, a[, x] modes with b, +, '
                  'and U (only with r) options. '
                  'See http://docs.python.org/2/library/functions.html#open'),
        'W1502': ('Using datetime.time in a boolean context.',
                  'boolean-datetime',
                  'Using datetime.time in a boolean context can hide '
                  'subtle bugs when the time they represent matches '
                  'midnight UTC. This behaviour was fixed in Python 3.5. '
                  'See http://bugs.python.org/issue13936 for reference.',
                  {'maxversion': (3, 5)}),
        'W1503': ('Redundant use of %s with constant '
                  'value %r',
                  'redundant-unittest-assert',
                  'The first argument of assertTrue and assertFalse is '
                  'a condition. If a constant is passed as parameter, that '
                  'condition will be always true. In this case a warning '
                  'should be emitted.'),
        'W1504': ('Using type() instead of isinstance() for a typecheck.',
                  'unidiomatic-typecheck',
                  'The idiomatic way to perform an explicit typecheck in '
                  'Python is to use isinstance(x, Y) rather than '
                  'type(x) == Y, type(x) is Y. Though there are unusual '
                  'situations where these give different results.')
    }

    @utils.check_messages('bad-open-mode', 'redundant-unittest-assert')
    def visit_callfunc(self, node):
        """Visit a CallFunc node."""
        if hasattr(node, 'func'):
            infer = helpers.safe_infer(node.func)
            if infer:
                if infer.root().name == OPEN_MODULE:
                    if getattr(node.func, 'name', None) in ('open', 'file'):
                        self._check_open_mode(node)
                if infer.root().name == 'unittest.case':
                    self._check_redundant_assert(node, infer)

    @utils.check_messages('boolean-datetime')
    def visit_unaryop(self, node):
        if node.op == 'not':
            self._check_datetime(node.operand)

    @utils.check_messages('boolean-datetime')
    def visit_if(self, node):
        self._check_datetime(node.test)

    @utils.check_messages('boolean-datetime')
    def visit_ifexp(self, node):
        self._check_datetime(node.test)

    @utils.check_messages('boolean-datetime')
    def visit_boolop(self, node):
        for value in node.values:
            self._check_datetime(value)

    @utils.check_messages('unidiomatic-typecheck')
    def visit_compare(self, node):
        operator, right = node.ops[0]
        if operator in TYPECHECK_COMPARISON_OPERATORS:
            left = node.left
            if _is_one_arg_pos_call(left):
                self._check_type_x_is_y(node, left, operator, right)

    def _check_redundant_assert(self, node, infer):
        if (isinstance(infer, astroid.BoundMethod) and
                node.args and isinstance(node.args[0], astroid.Const) and
                infer.name in ['assertTrue', 'assertFalse']):
            self.add_message('redundant-unittest-assert',
                             args=(infer.name, node.args[0].value, ),
                             node=node)

    def _check_datetime(self, node):
        """ Check that a datetime was infered.
        If so, emit boolean-datetime warning.
        """
        try:
            infered = next(node.infer())
        except astroid.InferenceError:
            return
        if (isinstance(infered, Instance) and
                infered.qname() == 'datetime.time'):
            self.add_message('boolean-datetime', node=node)

    def _check_open_mode(self, node):
        """Check that the mode argument of an open or file call is valid."""
        try:
            mode_arg = utils.get_argument_from_call(node, position=1,
                                                    keyword='mode')
        except utils.NoSuchArgumentError:
            return
        if mode_arg:
            mode_arg = helpers.safe_infer(mode_arg)
            if (isinstance(mode_arg, astroid.Const)
                    and not _check_mode_str(mode_arg.value)):
                self.add_message('bad-open-mode', node=node,
                                 args=mode_arg.value)

    def _check_type_x_is_y(self, node, left, operator, right):
        """Check for expressions like type(x) == Y."""
        left_func = helpers.safe_infer(left.func)
        if not (isinstance(left_func, astroid.Class)
                and left_func.qname() == TYPE_QNAME):
            return

        if operator in ('is', 'is not') and _is_one_arg_pos_call(right):
            right_func = helpers.safe_infer(right.func)
            if (isinstance(right_func, astroid.Class)
                    and right_func.qname() == TYPE_QNAME):
                # type(x) == type(a)
                right_arg = helpers.safe_infer(right.args[0])
                if not isinstance(right_arg, LITERAL_NODE_TYPES):
                    # not e.g. type(x) == type([])
                    return
        self.add_message('unidiomatic-typecheck', node=node)


def register(linter):
    """required method to auto register this checker """
    linter.register_checker(StdlibChecker(linter))