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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_empty_str(node):
- return isinstance(node, astroid.Const) and node.value == ''
-
-
- class CompareToEmptyStringChecker(checkers.BaseChecker):
- """Checks for comparisons to empty string.
- Most of the times you should use the fact that empty strings are false.
- An exception to this rule is when an empty string value is allowed in the program
- and has a different meaning than None!
- """
-
- __implements__ = (interfaces.IAstroidChecker,)
-
- # configuration section name
- name = 'compare-to-empty-string'
- msgs = {'C1901': ('Avoid comparisons to empty string',
- 'compare-to-empty-string',
- 'Used when Pylint detects comparison to an empty string constant.'),
- }
-
- priority = -2
- options = ()
-
- @utils.check_messages('compare-to-empty-string')
- 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
-
- # x ?? ""
- if _is_constant_empty_str(op_1) and op_2 in _operators:
- error_detected = True
- # '' ?? X
- elif op_2 in _operators and _is_constant_empty_str(op_3):
- error_detected = True
-
- if error_detected:
- self.add_message('compare-to-empty-string', node=node)
-
-
- def register(linter):
- """Required method to auto register this checker."""
- linter.register_checker(CompareToEmptyStringChecker(linter))
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