Some design and add doc to give an idea of the design before actual implementation

Author: Pierre-Sassoulas

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

@@ -0,0 +1 @@
+mindless_anarchy = 1504e5  # [bad-float-notation]

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

@@ -0,0 +1,3 @@
+exponent_not_multiple_of_three = 123e4  # [bad-float-notation]
+base_not_between_one_and_a_thousand = 12345e6  # [bad-float-notation]
+above_threshold_without_exponent = 10000000  # [bad-float-notation]

doc/data/messages/b/bad-float-notation/bad/pep515.py

@@ -0,0 +1,3 @@
+not_grouped_by_three = 1_23_456_7_89  # [bad-float-notation]
+mixing_with_exponent = 1_23_4_5_67_8e9  # [bad-float-notation]
+above_threshold_without_grouping = 123456789  # [bad-float-notation]

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

@@ -0,0 +1,2 @@
+base_not_between_one_and_10 = 10e3  # [bad-float-notation]
+above_threshold_without_exponent = 10000000  # [bad-float-notation]

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

@@ -0,0 +1,2 @@
+exponent_multiple_of_three = 1.23e6
+base_between_one_and_a_thousand = 12.345e9  # [bad-float-notation]

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

@@ -0,0 +1,3 @@
+scientific_notation = 1.504e8
+engineering_notation = 150.4e6
+underscore_notation = 150_400_000

doc/data/messages/b/bad-float-notation/good/pep515.py

@@ -0,0 +1,3 @@
+proper_grouping = 123_456_789
+scientific_notation = 1.2345678e16
+engineering_notation = 12.345678e15

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

@@ -0,0 +1,2 @@
+base_between_one_and_10 = 1e4
+above_threshold_with_exponent = 1e7

doc/user_guide/checkers/features.rst

@@ -557,6 +557,10 @@ Format checker Messages
   Used when there is different newline than expected.
 :superfluous-parens (C0325): *Unnecessary parens after %r keyword*
   Used when a single item in parentheses follows an if, for, or other keyword.
+:bad-float-notation (C0329): *float literal 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.
 
 
 Imports checker

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