On 8 Mar, 06:02 pm, [EMAIL PROTECTED] wrote:
On Thu, Mar 08, 2007 at 06:54:30PM +0100, "Martin v. L?wis" wrote:
back_name = splitext(name[0]) + '.bak'
back_name = splitext(name)[0] + '.bak'
This is really totally secondary to the point I actually care about, but
seeing this antipattern bandied about as a reason to make the change is
starting to bother me.
There's no way to "fix" this idiom. Forget the corner case; what if you
have a foobar.py and a foobar.txt in the same directory? This is not at
all uncommon, and your "backup" function here will clobber those files
in any case.
Furthermore, although the module documentation is vague, the docstring
for splitext specifically says "either part may be empty" and "extension
is everything from the last dot to the end". Again, this is a case of
needing a function designed to perform a specific task, and instead
relying on half-broken idioms which involve other functions.
make_backup_filename(x) might *use* splitext, but it is not what
splitext is *for*. A correct implementation which did use splitext
would look like this:
def make_backup_filename(filename):
base, extension = splitext(filename)
return base + '.bak' + extension
although personally I would probably prefer this:
def make_backup_filename(filename):
return filename + '.bak'
If the behavior of the old code is going to be buggy in any case, it
might as well be buggy and consistent. Consider a program that
periodically makes and then cleans up backup files, and uses the
"correct" splitext-using function above. Perhaps .cshrc.bak makes more
sense than .bak.cshrc to some people, but that means that on a system
where python is upgraded, .bak.cshrc will be left around forever. Even
on a program whose functionality is improved by this change, the
incompatibility between versions might create problems.
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