Christoph Zwerschke a écrit :
In Python programs, you will quite frequently find code like the
following for removing a certain prefix from a string:
if url.startswith('http://'):
url = url[7:]
DRY/SPOT violation. Should be written as :
prefix = 'http://'
if url.startswith(prefix):
url = url[len(prefix):]
(snip)
My problem with this is that it's cumbersome and error prone to count
the number of chars of the prefix or suffix.
cf above
If you want to change it
from 'http://' to 'https://', you must not forget to change the 7 to 8.
If you write len('http://') instead of the 7, you see this is actually
a DRY problem.
cf above
Things get even worse if you have several prefixes to consider:
if url.startswith('http://'):
url = url[7:]
elif url.startswith('https://'):
url = url[8:]
You can't take use of url.startswith(('http://', 'https://')) here.
for prefix in ('http://', 'https://'):
if url.startswith(prefix):
url = url[len(prefix):]
break
For most complex use case, you may want to consider regexps,
specifically re.sub:
>>> import re
>>> pat = re.compile(r"(^https?://|\.txt$)")
>>> urls = ['http://toto.com', 'https://titi.com', 'tutu.com',
'file://tata.txt']
>>> [pat.sub('', u) for u in urls]
['toto.com', 'titi.com', 'tutu.com', 'file://tata']
Not to dismiss your suggestion, but I thought you might like to know how
to solve your problem with what's currently available !-)
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