Nick Coghlan added the comment:
My recollection is that fromhex() ignores spaces to account for particularly
common ways of formatting hex numbers as space separated groups:
"CAFE F00D"
"CAFEF00D CAFEF00D CAFEF00D"
"CA FE F0 0D"
etc
Those show up even in structured hexadecimal data (like hex editor output and
memory dumps in log files).
That recollection is supported by the example and specification of specifically
"[0-9a-fA-F ]" in PEP 358 (https://www.python.org/dev/peps/pep-0358/) that
guided Georg Brandl's initial implementation in
http://bugs.python.org/issue1669379
Generally speaking, the type level string parsers *aren't* permissive when it
comes to their whitespace handling - if they allow whitespace at all, it's
usually only at the beginning or end, where it gets ignored (hence the PEP for
3.6 to allow underscores in both numeric literals and in the numeric
constructors).
=====================
>>> float(" 1.0")
1.0
>>> float("1.0 ")
1.0
>>> float("1 0")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: could not convert string to float: '1 0'
>>> float("1. 0")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: could not convert string to float: '1. 0'
>>> float("1 .0")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: could not convert string to float: '1 .0'
=====================
The general technique to strip whitespace from *any* input data before handing
it to a constructor relies on str.translate:
=====================
>>> import string
>>> _del_whitespace = str.maketrans('', '', string.whitespace)
>>> def clean_whitespace(text):
... return text.translate(_del_whitespace)
...
>>> clean_whitespace('CA FE\nF0\t0D')
'CAFEF00D'
=====================
(http://stackoverflow.com/questions/3739909/how-to-strip-all-whitespace-from-string
also points out `"".join(text.split())` as a clever one liner for a similar
outcome)
So I'm inclined to advise *against* making any changes here - the apparent
benefit is more a symptom of the fact that there isn't an immediately obvious
spelling of "strip all whitespace, including that between other characters,
from this string" that can be readily applied as an initial filter on the
incoming data.
(However, I do sometimes wonder if it would make sense to offer a
"str.stripall()" that defaulted to removing all whitespace, rather than
treating this purely as a particular use case for str.translate)
----------
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue28927>
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