def _to_literal(node: nodes.NodeNG) -> Any:
# Can raise SyntaxError or ValueError from ast.literal_eval
# Can raise AttributeError from node.as_string() as not all nodes have a visitor
# Is this the stupidest idea or the simplest idea?
return ast.literal_eval(node.as_string())
def _check_singleton_comparison(
self,
left_value: nodes.NodeNG,
right_value: nodes.NodeNG,
root_node: nodes.Compare,
checking_for_absence: bool = False,
) -> None:
"""Check if == or != is being used to compare a singleton value."""
singleton_values = (True, False, None)
def _is_singleton_const(node: nodes.NodeNG) -> bool:
return isinstance(node, nodes.Const) and any(
node.value is value for value in singleton_values
)
if _is_singleton_const(left_value):
singleton, other_value = left_value.value, right_value
elif _is_singleton_const(right_value):
singleton, other_value = right_value.value, left_value
else:
return
singleton_comparison_example = {False: "'{} is {}'", True: "'{} is not {}'"}
# True/False singletons have a special-cased message in case the user is
# mistakenly using == or != to check for truthiness
if singleton in {True, False}:
suggestion_template = (
"{} if checking for the singleton value {}, or {} if testing for {}"
)
truthiness_example = {False: "not {}", True: "{}"}
truthiness_phrase = {True: "truthiness", False: "falsiness"}
# Looks for comparisons like x == True or x != False
checking_truthiness = singleton is not checking_for_absence
suggestion = suggestion_template.format(
singleton_comparison_example[checking_for_absence].format(
left_value.as_string(), right_value.as_string()
),
singleton,
(
"'bool({})'"
if not utils.is_test_condition(root_node) and checking_truthiness
else "'{}'"
).format(
truthiness_example[checking_truthiness].format(
other_value.as_string()
)
),
truthiness_phrase[checking_truthiness],
)
else:
suggestion = singleton_comparison_example[checking_for_absence].format(
left_value.as_string(), right_value.as_string()
)
self.add_message(
"singleton-comparison",
node=root_node,
args=(f"'{root_node.as_string()}'", suggestion),
)