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76 lines
2.5 KiB
Python
76 lines
2.5 KiB
Python
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# Copyright (c) 2016 Alexander Todorov <atodorov@otb.bg>
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# Copyright (c) 2017-2018, 2020 Claudiu Popa <pcmanticore@gmail.com>
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# Copyright (c) 2019 Pierre Sassoulas <pierre.sassoulas@gmail.com>
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# Copyright (c) 2020 Anthony Sottile <asottile@umich.edu>
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# Licensed under the GPL: https://www.gnu.org/licenses/old-licenses/gpl-2.0.html
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# For details: https://github.com/PyCQA/pylint/blob/master/COPYING
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"""Looks for comparisons to empty string."""
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import itertools
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import astroid
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from pylint import checkers, interfaces
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from pylint.checkers import utils
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def _is_constant_empty_str(node):
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return isinstance(node, astroid.Const) and node.value == ""
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class CompareToEmptyStringChecker(checkers.BaseChecker):
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"""Checks for comparisons to empty string.
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Most of the times you should use the fact that empty strings are false.
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An exception to this rule is when an empty string value is allowed in the program
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and has a different meaning than None!
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"""
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__implements__ = (interfaces.IAstroidChecker,)
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# configuration section name
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name = "compare-to-empty-string"
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msgs = {
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"C1901": (
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"Avoid comparisons to empty string",
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"compare-to-empty-string",
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"Used when Pylint detects comparison to an empty string constant.",
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)
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}
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priority = -2
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options = ()
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@utils.check_messages("compare-to-empty-string")
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def visit_compare(self, node):
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_operators = ["!=", "==", "is not", "is"]
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# note: astroid.Compare has the left most operand in node.left
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# while the rest are a list of tuples in node.ops
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# the format of the tuple is ('compare operator sign', node)
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# here we squash everything into `ops` to make it easier for processing later
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ops = [("", node.left)]
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ops.extend(node.ops)
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ops = list(itertools.chain(*ops))
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for ops_idx in range(len(ops) - 2):
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op_1 = ops[ops_idx]
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op_2 = ops[ops_idx + 1]
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op_3 = ops[ops_idx + 2]
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error_detected = False
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# x ?? ""
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if _is_constant_empty_str(op_1) and op_2 in _operators:
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error_detected = True
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# '' ?? X
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elif op_2 in _operators and _is_constant_empty_str(op_3):
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error_detected = True
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if error_detected:
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self.add_message("compare-to-empty-string", node=node)
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def register(linter):
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"""Required method to auto register this checker."""
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linter.register_checker(CompareToEmptyStringChecker(linter))
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