The ValueError for converting an all-whitespace string to a float misleadingly displays it as the empty string #95605

Zeturic · 2022-08-03T18:34:55Z

Bug report

Actual behavior:

>>> float('\n')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: could not convert string to float: ''

Expected behavior:

>>> float('\n')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: could not convert string to float: '\n'

As long as the string isn't completely whitespace, it does display properly. For example:

>>> float('\nn')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: could not convert string to float: '\nn'

In addition to newlines, the same thing can be observed with tabs and carriage returns, or any combination of the three. I didn't test any additional whitespace characters, though they would likely behave the same way.

Your environment

CPython versions tested on: 3.10.5
Operating system and architecture: Windows 10 (64-bit)

mdickinson · 2022-08-04T17:59:18Z

Thanks for the report. This is caused by an unfortunate interaction between float_from_string_inner and PyOS_string_to_double. (The PyOS_string_to_double API leaves something to be desired, with its multi-channel reporting of errors, but it's part of the limited API so we can't change it.)

Specifically, after the PyOS_string_to_double call, if end == last in float_from_string_inner, then either the parse was successful, or the string being parsed was empty; conversely, if the parse was successful then end == last. So when we raise on end != last, we catch only parse failures on nonempty strings. The parse failure on an empty string just propagates the ValueError already raised in PyOS_string_to_double, which has an inferior error message.

#95665 should fix this.

…ace (GH-95665) This PR fixes the error message from float(s) in the case where s contains only whitespace.

…hitespace (pythonGH-95665) This PR fixes the error message from float(s) in the case where s contains only whitespace. (cherry picked from commit 97e9cfa) Co-authored-by: Mark Dickinson <dickinsm@gmail.com>

…ace (GH-95665) (GH-95859) This PR fixes the error message from float(s) in the case where s contains only whitespace. (cherry picked from commit 97e9cfa) Co-authored-by: Mark Dickinson <dickinsm@gmail.com>

…ace (GH-95665) (GH-95858) This PR fixes the error message from float(s) in the case where s contains only whitespace. (cherry picked from commit 97e9cfa) Co-authored-by: Mark Dickinson <dickinsm@gmail.com>

Zeturic added the type-bug An unexpected behavior, bug, or error label Aug 3, 2022

mdickinson mentioned this issue Aug 4, 2022

gh-95605: Fix float(s) error message when s contains only whitespace #95665

Merged

mdickinson added 3.11 3.10 3.12 labels Aug 5, 2022

mdickinson closed this as completed in #95665 Aug 10, 2022

This was referenced Aug 10, 2022

[3.11] gh-95605: Fix float(s) error message when s contains only whitespace (GH-95665) #95858

Merged

[3.10] gh-95605: Fix float(s) error message when s contains only whitespace (GH-95665) #95859

Merged

mdickinson added a commit that referenced this issue Aug 10, 2022

gh-95605: Fix float(s) error message when s contains only whitesp…

97e9cfa

…ace (GH-95665) This PR fixes the error message from float(s) in the case where s contains only whitespace.

Nov	DEC	Jan
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2021	2022	2023

The ValueError for converting an all-whitespace string to a float misleadingly displays it as the empty string #95605

The ValueError for converting an all-whitespace string to a float misleadingly displays it as the empty string #95605

Zeturic commented Aug 3, 2022

mdickinson commented Aug 4, 2022 •

edited

The ValueError for converting an all-whitespace string to a float misleadingly displays it as the empty string #95605

The ValueError for converting an all-whitespace string to a float misleadingly displays it as the empty string #95605

Comments

Zeturic commented Aug 3, 2022

Bug report

Your environment

mdickinson commented Aug 4, 2022 • edited

mdickinson commented Aug 4, 2022 •

edited