Re: strip() using strings instead of chars
Duncan Booth schrieb: if url.startswith('http://'): url = url[7:] If I came across this code I'd want to know why they weren't using urlparse.urlsplit()... Right, such code can have a smell since in the case of urls, file names, config options etc. there are specialized functions available. But I'm not sure whether the need for removing string prefix/suffixes in general is really so rare that we shouldn't worry to offer a simpler solution. -- Christoph -- http://mail.python.org/mailman/listinfo/python-list
Re: strip() using strings instead of chars
Christoph Zwerschke [EMAIL PROTECTED] wrote: Duncan Booth schrieb: if url.startswith('http://'): url = url[7:] If I came across this code I'd want to know why they weren't using urlparse.urlsplit()... Right, such code can have a smell since in the case of urls, file names, config options etc. there are specialized functions available. But I'm not sure whether the need for removing string prefix/suffixes in general is really so rare that we shouldn't worry to offer a simpler solution. One of the great things about Python is that it resists bloating the builtin classes with lots of methods that just seem like a good idea at the time. If a lot of people make a case for this function then it might get added, but I think it is unlikely given how simple it is to write a function to do this for yourself. -- http://mail.python.org/mailman/listinfo/python-list
strip() using strings instead of chars
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:] Similarly for stripping suffixes: if filename.endswith('.html'): filename = filename[:-5] My problem with this is that it's cumbersome and error prone to count the number of chars of the prefix or suffix. 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. 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. Here is another concrete example taken from the standard lib: if chars.startswith(BOM_UTF8): chars = chars[3:].decode(utf-8) This avoids hardcoding the BOM_UTF8, but its length is still hardcoded, and the programmer had to know it or look it up when writing this line. So my suggestion is to add another string method, say stripstr that behaves like strip, but instead of stripping *characters* strips *strings* (similarly for lstrip and rstrip). Then in the case above, you could simply write url = url.lstripstr('http://') or url = url.lstripstr(('http://', 'https://')). The new function would actually comprise the old strip function, you would have strip('aeiou') == stripstr(set('aeio')). Instead of a new function, we could also add another parameter to strip (lstrip, rstrip) for passing strings or changing the behavior, or we could create functions with the signature of startswith and endswith which instead of only checking whether the string starts or ends with the substring, remove the substring (startswith and endswith have additional start and end index parameters that may be useful). Or did I overlook anything and there is already a good idiom for this? Btw, in most other languages, strip is called trim and behaves like Python's strip, i.e. considers the parameter as a set of chars. There is one notable exception: In MySQL, trim behaves like stripstr proposed above (differently to SQLite, PostgreSQL and Oracle). -- Christoph -- http://mail.python.org/mailman/listinfo/python-list
Re: strip() using strings instead of chars
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 !-) -- http://mail.python.org/mailman/listinfo/python-list
Re: strip() using strings instead of chars
Bruno Desthuilliers schrieb: DRY/SPOT violation. Should be written as : prefix = 'http://' if url.startswith(prefix): url = url[len(prefix):] That was exactly my point. This formulation is a bit better, but it still violates DRY, because you need to type prefix two times. It is exactly this idiom that I see so often and that I wanted to simplify. Your suggestions work, but I somehow feel such a simple task should have a simpler formulation in Python, i.e. something like url = url.lstripstr(('http://', 'https://')) instead of for prefix in ('http://', 'https://'): if url.startswith(prefix): url = url[len(prefix):] break -- Christoph -- http://mail.python.org/mailman/listinfo/python-list
Re: strip() using strings instead of chars
On Fri, 11 Jul 2008 16:45:20 +0200, Christoph Zwerschke wrote: Bruno Desthuilliers schrieb: DRY/SPOT violation. Should be written as : prefix = 'http://' if url.startswith(prefix): url = url[len(prefix):] That was exactly my point. This formulation is a bit better, but it still violates DRY, because you need to type prefix two times. It is exactly this idiom that I see so often and that I wanted to simplify. Your suggestions work, but I somehow feel such a simple task should have a simpler formulation in Python, i.e. something like url = url.lstripstr(('http://', 'https://')) I would prefer a name like `remove_prefix()` instead of a variant with `strip` and abbreviations in it. Ciao, Marc 'BlackJack' Rintsch -- http://mail.python.org/mailman/listinfo/python-list
Re: strip() using strings instead of chars
Christoph Zwerschke [EMAIL PROTECTED] wrote: 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:] If I came across this code I'd want to know why they weren't using urlparse.urlsplit()... Similarly for stripping suffixes: if filename.endswith('.html'): filename = filename[:-5] ... and I'd want to know why os.path.splitext() wasn't appropriate here. My problem with this is that it's cumbersome and error prone to count the number of chars of the prefix or suffix. 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. 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. No you can't, so you definitely want to be parsing the URL properly. I can't actually think of a use for stripping off the scheme without either saving it somewhere or doing further parsing of the url. -- http://mail.python.org/mailman/listinfo/python-list