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feat: expand use-implicit-booleaness-not-len to catch len comparisons to 0 #10962

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feat: expand use-implicit-booleaness-not-len to catch len comparisons to 0 #10962

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34 changes: 34 additions & 0 deletions pylint/checkers/refactoring/implicit_booleaness_checker.py
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Original file line number Diff line number Diff line change
Expand Up @@ -173,11 +173,14 @@ def visit_unaryop(self, node: nodes.UnaryOp) -> None:
)

@utils.only_required_for_messages(
"use-implicit-booleaness-not-len",
"use-implicit-booleaness-not-comparison",
"use-implicit-booleaness-not-comparison-to-string",
"use-implicit-booleaness-not-comparison-to-zero",
)
def visit_compare(self, node: nodes.Compare) -> None:
if self.linter.is_message_enabled("use-implicit-booleaness-not-len"):
self._check_len_comparison_to_zero(node)
if self.linter.is_message_enabled("use-implicit-booleaness-not-comparison"):
self._check_use_implicit_booleaness_not_comparison(node)
if self.linter.is_message_enabled(
Expand All @@ -187,6 +190,37 @@ def visit_compare(self, node: nodes.Compare) -> None:
):
self._check_compare_to_str_or_zero(node)

def _check_len_comparison_to_zero(self, node: nodes.Compare) -> None:
"""Check for len(x) comparisons against literal zero."""
if len(node.ops) != 1:
return

operator, right = node.ops[0]
left = node.left

if (
utils.is_call_of_name(left, "len")
and _is_constant_zero(right)
and operator in ("==", "!=", ">", ">=", "<", "<=")
):
self.add_message(
"use-implicit-booleaness-not-len",
node=node,
confidence=HIGH,
)
return

if (
_is_constant_zero(left)
and utils.is_call_of_name(right, "len")
and operator in ("==", "!=", ">", ">=", "<", "<=")
):
self.add_message(
"use-implicit-booleaness-not-len",
node=node,
confidence=HIGH,
)

def _check_compare_to_str_or_zero(self, node: nodes.Compare) -> None:
# Skip check for chained comparisons
if len(node.ops) != 1:
Expand Down
37 changes: 26 additions & 11 deletions tests/functional/u/use/use_implicit_booleaness_not_len.py
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Original file line number Diff line number Diff line change
Expand Up @@ -14,22 +14,37 @@
if True or len('TEST'): # [use-implicit-booleaness-not-len]
pass

if len('TEST') == 0: # Should be fine
if len('TEST') == 0: # [use-implicit-booleaness-not-len]
pass

if len('TEST') < 1: # Should be fine
if len('TEST') < 1: # Should be fine (comparing to 1, not 0)
pass

if len('TEST') <= 0: # Should be fine
if len('TEST') <= 0: # [use-implicit-booleaness-not-len]
pass

if 1 > len('TEST'): # Should be fine
if 1 > len('TEST'): # Should be fine (comparing to 1, not 0)
pass

if 0 >= len('TEST'): # Should be fine
if 0 >= len('TEST'): # [use-implicit-booleaness-not-len]
pass

if z and len('TEST') == 0: # Should be fine
if len('TEST') > 0: # [use-implicit-booleaness-not-len]
pass

if len('TEST') != 0: # [use-implicit-booleaness-not-len]
pass

if 0 < len('TEST'): # [use-implicit-booleaness-not-len]
pass

if 0 == len('TEST'): # [use-implicit-booleaness-not-len]
pass

if 0 != len('TEST'): # [use-implicit-booleaness-not-len]
pass

if z and len('TEST') == 0: # [use-implicit-booleaness-not-len]
pass

if 0 == len('TEST') < 10: # Should be fine
Expand Down Expand Up @@ -73,16 +88,16 @@
while not len('TEST') and z: # [use-implicit-booleaness-not-len]
pass

assert len('TEST') > 0 # Should be fine
assert len('TEST') > 0 # [use-implicit-booleaness-not-len]

x = 1 if len('TEST') != 0 else 2 # Should be fine
x = 1 if len('TEST') != 0 else 2 # [use-implicit-booleaness-not-len]

f_o_o = len('TEST') or 42 # Should be fine

a = x and len(x) # Should be fine

def some_func():
return len('TEST') > 0 # Should be fine
return len('TEST') > 0 # [use-implicit-booleaness-not-len]

def github_issue_1325():
l = [1, 2, 3]
Expand Down Expand Up @@ -132,7 +147,7 @@ class ChildClassWithoutBool(ClassWithoutBool):
# pylint: disable=import-outside-toplevel
import numpy
numpy_array = numpy.array([0])
if len(numpy_array) > 0:
if len(numpy_array) > 0: # [use-implicit-booleaness-not-len]
print('numpy_array')
if len(numpy_array):
print('numpy_array')
Expand All @@ -143,7 +158,7 @@ class ChildClassWithoutBool(ClassWithoutBool):
pandas_df = pd.DataFrame()
if len(pandas_df):
print("this works, but pylint tells me not to use len() without comparison")
if len(pandas_df) > 0:
if len(pandas_df) > 0: # [use-implicit-booleaness-not-len]
print("this works and pylint likes it, but it's not the solution intended by PEP-8")
if pandas_df:
print("this does not work (truth value of dataframe is ambiguous)")
Expand Down
56 changes: 35 additions & 21 deletions tests/functional/u/use/use_implicit_booleaness_not_len.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -2,24 +2,38 @@ use-implicit-booleaness-not-len:4:3:4:14::Do not use `len(SEQUENCE)` without com
use-implicit-booleaness-not-len:7:3:7:18::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:HIGH
use-implicit-booleaness-not-len:11:9:11:34::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:INFERENCE
use-implicit-booleaness-not-len:14:11:14:22::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:INFERENCE
comparison-of-constants:39:3:39:28::"Comparison between constants: ""0 < 1"" has a constant value":HIGH
use-implicit-booleaness-not-len:56:5:56:16::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:INFERENCE
use-implicit-booleaness-not-len:61:5:61:20::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:HIGH
use-implicit-booleaness-not-len:64:6:64:17::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:INFERENCE
use-implicit-booleaness-not-len:67:6:67:21::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:HIGH
use-implicit-booleaness-not-len:70:12:70:23::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:INFERENCE
use-implicit-booleaness-not-len:73:6:73:21::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:HIGH
use-implicit-booleaness-not-len:96:11:96:20:github_issue_1331_v2:Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:INFERENCE
use-implicit-booleaness-not-len:99:11:99:20:github_issue_1331_v3:Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:INFERENCE
use-implicit-booleaness-not-len:102:17:102:26:github_issue_1331_v4:Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:INFERENCE
use-implicit-booleaness-not-len:104:9:104:15::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:INFERENCE
use-implicit-booleaness-not-len:105:9:105:20::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:INFERENCE
use-implicit-booleaness-not-len:124:11:124:34:github_issue_1879:Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:INFERENCE
use-implicit-booleaness-not-len:125:11:125:39:github_issue_1879:Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:INFERENCE
use-implicit-booleaness-not-len:126:11:126:24:github_issue_1879:Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:INFERENCE
use-implicit-booleaness-not-len:127:11:127:35:github_issue_1879:Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:HIGH
use-implicit-booleaness-not-len:129:11:129:41:github_issue_1879:Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:HIGH
use-implicit-booleaness-not-len:130:11:130:43:github_issue_1879:Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:INFERENCE
use-implicit-booleaness-not-len:171:11:171:42:github_issue_1879:Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:INFERENCE
undefined-variable:183:11:183:24:github_issue_4215:Undefined variable 'undefined_var':UNDEFINED
undefined-variable:185:11:185:25:github_issue_4215:Undefined variable 'undefined_var2':UNDEFINED
use-implicit-booleaness-not-len:17:3:17:19::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:HIGH
use-implicit-booleaness-not-len:23:3:23:19::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:HIGH
use-implicit-booleaness-not-len:29:3:29:19::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:HIGH
use-implicit-booleaness-not-len:32:3:32:18::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:HIGH
use-implicit-booleaness-not-len:35:3:35:19::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:HIGH
use-implicit-booleaness-not-len:38:3:38:18::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:HIGH
use-implicit-booleaness-not-len:41:3:41:19::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:HIGH
use-implicit-booleaness-not-len:44:3:44:19::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:HIGH
use-implicit-booleaness-not-len:47:9:47:25::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:HIGH
comparison-of-constants:54:3:54:28::"Comparison between constants: ""0 < 1"" has a constant value":HIGH
use-implicit-booleaness-not-len:71:5:71:16::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:INFERENCE
use-implicit-booleaness-not-len:76:5:76:20::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:HIGH
use-implicit-booleaness-not-len:79:6:79:17::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:INFERENCE
use-implicit-booleaness-not-len:82:6:82:21::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:HIGH
use-implicit-booleaness-not-len:85:12:85:23::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:INFERENCE
use-implicit-booleaness-not-len:88:6:88:21::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:HIGH
use-implicit-booleaness-not-len:91:7:91:22::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:HIGH
use-implicit-booleaness-not-len:93:9:93:25::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:HIGH
use-implicit-booleaness-not-len:100:11:100:26:some_func:Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:HIGH
use-implicit-booleaness-not-len:111:11:111:20:github_issue_1331_v2:Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:INFERENCE
use-implicit-booleaness-not-len:114:11:114:20:github_issue_1331_v3:Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:INFERENCE
use-implicit-booleaness-not-len:117:17:117:26:github_issue_1331_v4:Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:INFERENCE
use-implicit-booleaness-not-len:119:9:119:15::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:INFERENCE
use-implicit-booleaness-not-len:120:9:120:20::Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:INFERENCE
use-implicit-booleaness-not-len:139:11:139:34:github_issue_1879:Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:INFERENCE
use-implicit-booleaness-not-len:140:11:140:39:github_issue_1879:Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:INFERENCE
use-implicit-booleaness-not-len:141:11:141:24:github_issue_1879:Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:INFERENCE
use-implicit-booleaness-not-len:142:11:142:35:github_issue_1879:Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:HIGH
use-implicit-booleaness-not-len:144:11:144:41:github_issue_1879:Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:HIGH
use-implicit-booleaness-not-len:145:11:145:43:github_issue_1879:Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:INFERENCE
use-implicit-booleaness-not-len:150:7:150:27:github_issue_1879:Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:HIGH
use-implicit-booleaness-not-len:161:7:161:25:github_issue_1879:Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:HIGH
use-implicit-booleaness-not-len:186:11:186:42:github_issue_1879:Do not use `len(SEQUENCE)` without comparison to determine if a sequence is empty:INFERENCE
undefined-variable:198:11:198:24:github_issue_4215:Undefined variable 'undefined_var':UNDEFINED
undefined-variable:200:11:200:25:github_issue_4215:Undefined variable 'undefined_var2':UNDEFINED
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