def visit_unaryop(self, node: nodes.UnaryOp) -> None:
"""`not len(S)` must become `not S` regardless if the parent block
is a test condition or something else (boolean expression)
e.g. `if not len(S):`"""
if (isinstance(node, nodes.UnaryOp) and node.op == "not"
and utils.is_call_of_name(node.operand, "len")):
self.add_message("len-as-condition", node=node)
def visit_call(self, node):
# a len(S) call is used inside a test condition
# could be if, while, assert or if expression statement
# e.g. `if len(S):`
if not utils.is_call_of_name(node, "len"):
return
# the len() call could also be nested together with other
# boolean operations, e.g. `if z or len(x):`
parent = node.parent
while isinstance(parent, astroid.BoolOp):
parent = parent.parent
# we're finally out of any nested boolean operations so check if
# this len() call is part of a test condition
if not utils.is_test_condition(node, parent):
return
len_arg = node.args[0]
generator_or_comprehension = (ListComp, SetComp, DictComp, GeneratorExp)
if isinstance(len_arg, generator_or_comprehension):
# The node is a generator or comprehension as in len([x for x in ...])
self.add_message("len-as-condition", node=node)
return
instance = next(len_arg.infer())
mother_classes = self.base_classes_of_node(instance)
affected_by_pep8 = any(
t in mother_classes for t in ["str", "tuple", "list", "set"]
)
if "range" in mother_classes or (
affected_by_pep8 and not self.instance_has_bool(instance)
):
self.add_message("len-as-condition", node=node)
def visit_call(self, node):
# a len(S) call is used inside a test condition
# could be if, while, assert or if expression statement
# e.g. `if len(S):`
if utils.is_call_of_name(node, "len"):
# the len() call could also be nested together with other
# boolean operations, e.g. `if z or len(x):`
parent = node.parent
while isinstance(parent, astroid.BoolOp):
parent = parent.parent
# we're finally out of any nested boolean operations so check if
# this len() call is part of a test condition
if utils.is_test_condition(node, parent):
self.add_message("len-as-condition", node=node)
def visit_call(self, node: nodes.Call) -> None:
# a len(S) call is used inside a test condition
# could be if, while, assert or if expression statement
# e.g. `if len(S):`
if not utils.is_call_of_name(node, "len"):
return
# the len() call could also be nested together with other
# boolean operations, e.g. `if z or len(x):`
parent = node.parent
while isinstance(parent, nodes.BoolOp):
parent = parent.parent
# we're finally out of any nested boolean operations so check if
# this len() call is part of a test condition
if not utils.is_test_condition(node, parent):
return
len_arg = node.args[0]
generator_or_comprehension = (
nodes.ListComp,
nodes.SetComp,
nodes.DictComp,
nodes.GeneratorExp,
)
if isinstance(len_arg, generator_or_comprehension):
# The node is a generator or comprehension as in len([x for x in ...])
self.add_message("use-implicit-booleaness-not-len", node=node)
return
try:
instance = next(len_arg.infer())
except astroid.InferenceError:
# Probably undefined-variable, abort check
return
mother_classes = self.base_classes_of_node(instance)
affected_by_pep8 = any(
t in mother_classes for t in ("str", "tuple", "list", "set")
)
if "range" in mother_classes or (
affected_by_pep8 and not self.instance_has_bool(instance)
):
self.add_message("use-implicit-booleaness-not-len", node=node)