[consider-math-not-float] Add a check for float("inf"), float("nan") and float("typos") (#10621)

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

Author: Pierre-Sassoulas

doc/data/messages/c/consider-math-not-float/bad.py

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

doc/data/messages/c/consider-math-not-float/details.rst

@@ -0,0 +1,40 @@
+This is an extension check because the typing advantage could be fixed.
+
+Regarding performance, float("nan") and float("inf") are slower than their counterpart math.inf and math.nan by a factor of 4 after the initial import of math.
+
+.. code-block:: python
+
+    import math
+    import timeit
+
+    time_math_inf = timeit.timeit('math.nan', globals=globals(), number=10**8)
+    print(f'math.nan: {time_math_inf:.2f} seconds')
+
+    import timeit
+    time_inf_str = timeit.timeit('float("nan")', number=10**8)
+    print(f'float("nan"): {time_inf_str:.2f} seconds')
+
+Result::
+
+    math.nan: 1.24 seconds
+    float("nan"): 5.15 seconds
+
+But if we take the initial import into account it's worse.
+
+.. code-block:: python
+
+    import timeit
+
+    time_math_inf = timeit.timeit('import math;math.nan', globals=globals(), number=10**8)
+    print(f'math.nan: {time_math_inf:.2f} seconds')
+
+    import timeit
+    time_inf_str = timeit.timeit('float("nan")', number=10**8)
+    print(f'float("nan"): {time_inf_str:.2f} seconds')
+
+Result::
+
+    math.nan: 9.08 seconds
+    float("nan"): 5.33 seconds
+
+So the decision depends on how and how often you need to use it and what matter to you.

doc/data/messages/c/consider-math-not-float/good.py

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

doc/data/messages/c/consider-math-not-float/pylintrc

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

doc/user_guide/checkers/extensions.rst

@@ -88,6 +88,10 @@ Code Style checker Messages
   'typing.NamedTuple' uses the well-known 'class' keyword with type-hints for
   readability (it's also faster as it avoids an internal exec call). Disabled
   by default!
+:consider-math-not-float (R6106): *Consider %smath.%s instead of %s*
+  Using math.inf or math.nan permits to benefit from typing and it is up to 4
+  times faster than a float call (after the initial import of math). This check
+  also catches typos in float calls as a side effect.
 
 
 .. _pylint.extensions.comparison_placement:

doc/user_guide/checkers/features.rst

@@ -689,11 +689,11 @@ Match Statements checker Messages
 :invalid-match-args-definition (E1902): *`__match_args__` must be a tuple of strings.*
   Emitted if `__match_args__` isn't a tuple of strings required for match.
 :too-many-positional-sub-patterns (E1903): *%s expects %d positional sub-patterns (given %d)*
-  Emitted when the number of allowed positional sub-patterns exceeds the
-  number of allowed sub-patterns specified in `__match_args__`.
+  Emitted when the number of allowed positional sub-patterns exceeds the number
+  of allowed sub-patterns specified in `__match_args__`.
 :multiple-class-sub-patterns (E1904): *Multiple sub-patterns for attribute %s*
-  Emitted when there is more than one sub-pattern for a specific attribute in
-  a class pattern.
+  Emitted when there is more than one sub-pattern for a specific attribute in a
+  class pattern.
 :match-class-bind-self (R1905): *Use '%s() as %s' instead*
   Match class patterns are faster if the name binding happens for the whole
   pattern and any lookup for `__match_args__` can be avoided.

doc/user_guide/messages/messages_overview.rst

@@ -491,6 +491,7 @@ All messages in the refactor category:
    refactor/condition-evals-to-constant
    refactor/confusing-consecutive-elif
    refactor/consider-alternative-union-syntax
+   refactor/consider-math-not-float
    refactor/consider-merging-isinstance
    refactor/consider-refactoring-into-while-condition
    refactor/consider-swap-variables

doc/whatsnew/fragments/10621.new_check

@@ -0,0 +1,8 @@
+Add a ``consider-math-not-float`` message. ``float("nan")`` and ``float("inf")`` are slower
+than their counterpart ``math.inf`` and ``math.nan`` by a factor of 4 (notwithstanding
+the initial import of math) and they are also not well typed when using mypy.
+This check also catches typos in float calls as a side effect.
+
+The :ref:`pylint.extensions.code_style` need to be activated for this check to work.
+
+Refs #10621

pylint/extensions/code_style.py

@@ -4,6 +4,7 @@
 
 from __future__ import annotations
 
+import difflib
 from typing import TYPE_CHECKING, TypeGuard, cast
 
 from astroid import nodes
@@ -74,6 +75,13 @@ class CodeStyleChecker(BaseChecker):
                 "default_enabled": False,
             },
         ),
+        "R6106": (
+            "Consider %smath.%s instead of %s",
+            "consider-math-not-float",
+            "Using math.inf or math.nan permits to benefit from typing and it is up "
+            "to 4 times faster than a float call (after the initial import of math). "
+            "This check also catches typos in float calls as a side effect.",
+        ),
     }
     options = (
         (
@@ -101,14 +109,42 @@ 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", "consider-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
+                    )
+                ):
+                    value = node.args[0].value.lower()
+                    math_call: str
+                    if "nan" in value:
+                        math_call = "nan"
+                    elif "inf" in value:
+                        math_call = "inf"
+                    else:
+                        math_call = difflib.get_close_matches(
+                            value, ["inf", "nan"], n=1, cutoff=0
+                        )[0]
+                    minus = "-" if math_call == "inf" and value.startswith("-") else ""
+                    self.add_message(
+                        "consider-math-not-float",
+                        node=node,
+                        args=(minus, math_call, 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 +1,18 @@
+"""Functional test for consider-math-not-float."""
+
+inf_float = float("inf")  # [consider-math-not-float]
+neg_inf_float = float('-inf')  # [consider-math-not-float]
+pos_inf_float = float("+inf")  # [consider-math-not-float]
+infinity_float = float("infinity")  # [consider-math-not-float]
+neg_infinity_float = float("-infinity")  # [consider-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")  # [consider-math-not-float]
+invalid_float_call = float("in", base=10)  # [consider-math-not-float]
+nan_float = float("nan")  # [consider-math-not-float]
+neg_nan_float = float("-nan")  # [consider-math-not-float]
+pos_nan_float = float("+nan")  # [consider-math-not-float]
+upper_nan_float = float("NaN")  # [consider-math-not-float]
+typo_nan_float = float("nani")  # [consider-math-not-float]
+other_typo_nan_float = float("nna")  # [consider-math-not-float]