[issue39524] Escape sequences in doc string of ast._pad_whitespace

[mpheath]

New submission from mpheath <mpheath at tpg.com.au>:

In the ast module, a function named _pad_whitespace has a doc string with escape sequences of \f and \t.

The current doc string from Lib/ast.py:305 is:

    """Replace all chars except '\f\t' in a line with spaces."""

Example of doc string output in a REPL:

    Python 3.8.0 (tags/v3.8.0:fa919fd, Oct 14 2019, 19:37:50) [MSC v.1916 64 bit (AMD64)] on win32
    Type "help", "copyright", "credits" or "license" for more information.
    >>> import ast
    >>> import inspect
    >>> inspect.getdoc(ast._pad_whitespace)
    "Replace all chars except '\x0c     ' in a line with spaces."
    >>>

The \x0c is the formfeed and the '     ' (5 spaces) was the tab.

It is my understanding that the output should be:

    "Replace all chars except '\f\t' in a line with spaces."

I would expect the source to be:

    """Replace all chars except '\\f\\t' in a line with spaces."""

or perhaps a raw string:

    r"""Replace all chars except '\f\t' in a line with spaces."""

The current Lib/ast.py:305 is Python 3.9.0 alpha 3 though the issue is also in Python 3.8.0 and 3.8.1 with 3.8/Lib/ast.py:227 .
Python 3.7.4 3.7/Lib/ast.py does not have the function _pad_whitespace as it appears major code changes occurred in the ast module with Python 3.8.0.

----------
messages: 361203
nosy: mpheath
priority: normal
severity: normal
status: open
title: Escape sequences in doc string of ast._pad_whitespace
type: behavior
versions: Python 3.8, Python 3.9

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue39524>
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