Repository navigation
The ValueError for converting an all-whitespace string to a float misleadingly displays it as the empty string #95605
Description
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)
Activity
mdickinson commentedon Aug 4, 2022
Thanks for the report. This is caused by an unfortunate interaction between
float_from_string_innerandPyOS_string_to_double. (ThePyOS_string_to_doubleAPI 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_doublecall, ifend == lastinfloat_from_string_inner, then either the parse was successful, or the string being parsed was empty; conversely, if the parse was successful thenend == last. So when we raise onend != last, we catch only parse failures on nonempty strings. The parse failure on an empty string just propagates theValueErroralready raised inPyOS_string_to_double, which has an inferior error message.#95665 should fix this.
gh-95605: Fix `float(s)` error message when `s` contains only whitesp…
pythongh-95605: Fix `float(s)` error message when `s` contains only w…
pythongh-95605: Fix `float(s)` error message when `s` contains only w…
gh-95605: Fix `float(s)` error message when `s` contains only whitesp…
gh-95605: Fix `float(s)` error message when `s` contains only whitesp…