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# -*- coding: utf-8 -*-
# Copyright (c) 2016 Alexander Todorov <atodorov@otb.bg>
# Copyright (c) 2017 Claudiu Popa <pcmanticore@gmail.com>
# Licensed under the GPL: https://www.gnu.org/licenses/old-licenses/gpl-2.0.html
# For details: https://github.com/PyCQA/pylint/blob/master/COPYING
"""Looks for comparisons to empty string."""
import itertools
import astroid
from pylint import interfaces
from pylint import checkers
from pylint.checkers import utils
def _is_constant_zero(node):
return isinstance(node, astroid.Const) and node.value == 0
class CompareToZeroChecker(checkers.BaseChecker):
"""Checks for comparisons to zero.
Most of the times you should use the fact that integers with a value of 0 are false.
An exception to this rule is when 0 is allowed in the program and has a
different meaning than None!
"""
__implements__ = (interfaces.IAstroidChecker,)
# configuration section name
name = 'compare-to-zero'
msgs = {'C2001': ('Avoid comparisons to zero',
'compare-to-zero',
'Used when Pylint detects comparison to a 0 constant.'),
}
priority = -2
options = ()
@utils.check_messages('compare-to-zero')
def visit_compare(self, node):
_operators = ['!=', '==', 'is not', 'is']
# note: astroid.Compare has the left most operand in node.left
# while the rest are a list of tuples in node.ops
# the format of the tuple is ('compare operator sign', node)
# here we squash everything into `ops` to make it easier for processing later
ops = [('', node.left)]
ops.extend(node.ops)
ops = list(itertools.chain(*ops))
for ops_idx in range(len(ops) - 2):
op_1 = ops[ops_idx]
op_2 = ops[ops_idx + 1]
op_3 = ops[ops_idx + 2]
error_detected = False
# 0 ?? X
if _is_constant_zero(op_1) and op_2 in _operators + ['<']:
error_detected = True
# X ?? 0
elif op_2 in _operators + ['>'] and _is_constant_zero(op_3):
error_detected = True
if error_detected:
self.add_message('compare-to-zero', node=node)
def register(linter):
"""Required method to auto register this checker."""
linter.register_checker(CompareToZeroChecker(linter))
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