[use-math-not-float] Add a check for float(inf) and float(nan)

Co-authored-by: Morwenn <[email protected]>

Author: Pierre-Sassoulas

doc/data/messages/u/use-math-not-float/bad.py

@@ -0,0 +1 @@
+swag = float("inf")  # [use-math-not-float]

doc/data/messages/u/use-math-not-float/good.py

@@ -0,0 +1,3 @@
+import math
+
+swag = math.inf

doc/data/messages/u/use-math-not-float/pylintrc

@@ -0,0 +1,2 @@
+[MAIN]
+load-plugins=pylint.extensions.code_style

doc/whatsnew/fragments/10621.new_check

@@ -0,0 +1,7 @@
+Add a ``use-math-not-float`` message. float("nan") and float("inf") are slower
+than their counterpart ``math.inf`` and ``math.nan`` by a factor of 4 and they
+are also not well typed when using mypy.
+
+The :ref:`pylint.extensions.code_style` need to be activated for this check to work.
+
+Refs #10621

pylint/extensions/code_style.py

@@ -74,6 +74,13 @@ class CodeStyleChecker(BaseChecker):
                 "default_enabled": False,
             },
         ),
+        "R6106": (
+            "%smath.%s is preferable to %s",
+            "use-math-not-float",
+            "Using math.inf or math.nan permits to benefit from typing "
+            "and it is 4 time faster than a float call.\n"
+            "Requires 'import math' in the file.",
+        ),
     }
     options = (
         (
@@ -101,14 +108,35 @@ def open(self) -> None:
             or self.linter.config.max_line_length
         )
 
-    @only_required_for_messages("prefer-typing-namedtuple")
+    @only_required_for_messages("prefer-typing-namedtuple", "use-math-not-float")
     def visit_call(self, node: nodes.Call) -> None:
         if self._py36_plus:
             called = safe_infer(node.func)
-            if called and called.qname() == "collections.namedtuple":
+            if not called:
+                return
+            if called.qname() == "collections.namedtuple":
                 self.add_message(
                     "prefer-typing-namedtuple", node=node, confidence=INFERENCE
                 )
+            elif called.qname() == "builtins.float":
+                if (
+                    node.args
+                    and isinstance(node.args[0], nodes.Const)
+                    and isinstance(node.args[0].value, str)
+                    and any(
+                        c.isalpha() and c.lower() != "e" for c in node.args[0].value
+                    )
+                ):
+                    is_nan = "nan" in node.args[0].value.lower()
+                    minus = (
+                        "-" if not is_nan and node.args[0].value.startswith("-") else ""
+                    )
+                    self.add_message(
+                        "use-math-not-float",
+                        node=node,
+                        args=(minus, "nan" if is_nan else "inf", node.as_string()),
+                        confidence=INFERENCE,
+                    )
 
     @only_required_for_messages("consider-using-namedtuple-or-dataclass")
     def visit_dict(self, node: nodes.Dict) -> None:

tests/functional/ext/code_style/cs_use_math_not_float.py

@@ -0,0 +1,16 @@
+"""Functional test for use-math-not-float."""
+
+inf_float = float("inf")  # [use-math-not-float]
+neg_inf_float = float('-inf')  # [use-math-not-float]
+pos_inf_float = float("+inf")  # [use-math-not-float]
+infinity_float = float("infinity")  # [use-math-not-float]
+neg_infinity_float = float("-infinity")  # [use-math-not-float]
+large_exp_float = float("1e1000")
+neg_large_exp_float = float("-1e1000")
+very_large_exp_float = float("2.5E9999")
+invalid_inf_float = float("in")  # [use-math-not-float]
+invalid_float_call = float("in", base=10)  # [use-math-not-float]
+nan_float = float("nan")  # [use-math-not-float]
+neg_nan_float = float("-nan")  # [use-math-not-float]
+pos_nan_float = float("+nan")  # [use-math-not-float]
+upper_nan_float = float("NaN")  # [use-math-not-float]

tests/functional/ext/code_style/cs_use_math_not_float.rc

@@ -0,0 +1,3 @@
+[MAIN]
+load-plugins=pylint.extensions.code_style
+enable=use-math-not-float

tests/functional/ext/code_style/cs_use_math_not_float.txt

@@ -0,0 +1,11 @@
+use-math-not-float:3:12:3:24::math.inf is preferable to float('inf'):INFERENCE
+use-math-not-float:4:16:4:29::-math.inf is preferable to float('-inf'):INFERENCE
+use-math-not-float:5:16:5:29::math.inf is preferable to float('+inf'):INFERENCE
+use-math-not-float:6:17:6:34::math.inf is preferable to float('infinity'):INFERENCE
+use-math-not-float:7:21:7:39::-math.inf is preferable to float('-infinity'):INFERENCE
+use-math-not-float:11:20:11:31::math.inf is preferable to float('in'):INFERENCE
+use-math-not-float:12:21:12:41::math.inf is preferable to float('in', base=10):INFERENCE
+use-math-not-float:13:12:13:24::math.nan is preferable to float('nan'):INFERENCE
+use-math-not-float:14:16:14:29::math.nan is preferable to float('-nan'):INFERENCE
+use-math-not-float:15:16:15:29::math.nan is preferable to float('+nan'):INFERENCE
+use-math-not-float:16:18:16:30::math.nan is preferable to float('NaN'):INFERENCE