[format check] Misleading scientific, engineering, or underscore grouping notations in float

doc/data/messages/b/bad-float-notation/bad.py

@@ -0,0 +1,5 @@
+mindless_anarchy = 15_04e05  # [bad-float-notation]
+
+this_checker_creation_time = 1751760000.0  # [bad-float-notation]
+
+small_float = 9.0e2  # [bad-float-notation]

doc/data/messages/b/bad-float-notation/details.rst

@@ -0,0 +1,6 @@
+There's 4 options associated with this message:
+- ``strict-engineering-notation``
+- ``strict-scientific-notation``
+- ``strict-underscore-notation``
+- ``float-notation-threshold``
+By default we allow all three standard and the threshold is 10e6.

doc/data/messages/b/bad-float-notation/good.py

@@ -0,0 +1,7 @@
+engineering_notation = 150.4e6
+scientific_notation = 1.504e8
+pep515_notation = 150_400_000.0
+
+this_checker_creation_time = (3600 * 24 * 365 * 55) + ((6 * 30 + 20) * 3600 * 24)
+
+small_float = 90.0

doc/data/messages/b/bad-float-notation/related.rst

@@ -0,0 +1 @@
+- `PEP 515 <https://docs.python.org/3/library/string.html#formatstrings>`_

doc/test_messages_documentation.py

@@ -173,7 +173,9 @@ def _runTest(self) -> None:
             assert len(actual_messages_raw) >= len(bad_files), self.assert_message_bad(
                 bad_files, actual_messages_raw
             )
-        assert expected_messages == self._get_actual(actual_messages_raw)
+        actual = self._get_actual(actual_messages_raw)
+        assert_msg = f"Expected {expected_messages!r} and got {actual!r} in {self._test_file[1]}."
+        assert expected_messages == actual, assert_msg
 
     def assert_message_good(self, messages: list[Message]) -> str:
         good = self._test_file[1]

doc/user_guide/checkers/features.rst

@@ -539,6 +539,10 @@ Format checker Messages
 :unnecessary-semicolon (W0301): *Unnecessary semicolon*
   Used when a statement is ended by a semi-colon (";"), which isn't necessary
   (that's python, not C ;).
+:bad-float-notation (C0329): *'%s' %s, and it should be written as '%s' instead*
+  Emitted when a number is written in a non-standard notation. The three
+  allowed notation above the threshold are the scientific notation, the
+  engineering notation, and the underscore grouping notation defined in PEP515.
 :missing-final-newline (C0304): *Final newline missing*
   Used when the last line in a file is missing a newline.
 :line-too-long (C0301): *Line too long (%s/%s)*

doc/user_guide/configuration/all-options.rst

@@ -879,6 +879,13 @@ Standard Checkers
 **Default:** ``""``
 
 
+--float-notation-threshold
+""""""""""""""""""""""""""
+*Threshold for float literals to be expected to be written using the scientific, engineering or underscore notation. If the absolute value of a float literal is greater than this value (or smaller than the inverse of this value for scientific and engineering notation), it will be checked.*
+
+**Default:**  ``1e6``
+
+
 --ignore-long-lines
 """""""""""""""""""
 *Regexp for a line that is allowed to be longer than the limit.*
@@ -928,6 +935,27 @@ Standard Checkers
 **Default:**  ``False``
 
 
+--strict-engineering-notation
+"""""""""""""""""""""""""""""
+*Only allow engineering notation for float literals with absolute value bigger than 'float-notation-threshold' or smallerthan the inverse of 'float-notation-threshold'.*
+
+**Default:**  ``False``
+
+
+--strict-scientific-notation
+""""""""""""""""""""""""""""
+*Only allow scientific notation for float literals with absolute value bigger than 'float-notation-threshold' or smallerthan the inverse of 'float-notation-threshold'.*
+
+**Default:**  ``False``
+
+
+--strict-underscore-notation
+""""""""""""""""""""""""""""
+*Only allow underscore notation for float literals bigger than 'float-notation-threshold'.*
+
+**Default:**  ``False``
+
+
 
 .. raw:: html
 
@@ -942,6 +970,8 @@ Standard Checkers
    # Possible choices: ['', 'LF', 'CRLF']
    expected-line-ending-format = ""
 
+   float-notation-threshold = 1000000.0
+
    ignore-long-lines = "^\\s*(# )?<?https?://\\S+>?$"
 
    indent-after-paren = 4
@@ -956,6 +986,12 @@ Standard Checkers
 
    single-line-if-stmt = false
 
+   strict-engineering-notation = false
+
+   strict-scientific-notation = false
+
+   strict-underscore-notation = false
+
 
 
 .. raw:: html

doc/user_guide/messages/messages_overview.rst

@@ -399,6 +399,7 @@ All messages in the convention category:
    convention/bad-classmethod-argument
    convention/bad-docstring-quotes
    convention/bad-file-encoding
+   convention/bad-float-notation
    convention/bad-mcs-classmethod-argument
    convention/bad-mcs-method-argument
    convention/consider-iterating-dictionary

doc/whatsnew/fragments/10425.feature

@@ -0,0 +1,3 @@
+Added a check for misleading scientific notations and use of underscore grouping in `float` literals.
+
+Refs #10425