[Python-ideas] String Subtraction (original) (raw)

Mike Meyer mwm-keyword-python.b4bdba at mired.org
Thu Oct 14 23:23:11 CEST 2010

On Thu, 14 Oct 2010 20:58:52 +0000 Dave Jakeman <davejakeman at hotmail.com> wrote:

I'm new to Python and this is my first suggestion, so please bear with me:

I believe there is a simple but useful string operation missing from Python: subtraction. This is best described by way of example: >>> "Mr Nesbit has learnt the first lesson of not being seen." - "Nesbit " 'Mr has learnt the first lesson of not being seen.' >>> "Can't have egg, bacon, spam and sausage without the spam." - " spam" 'Can't have egg, bacon, and sausage without the spam.' >>> "I'll bite your legs off!" - "arms" 'I'll bite your legs off!' If b and c were strings, then: a = b - c would be equivalent to:

The existing construct a = b.replace(c, '', 1)

The problem isn't that it's non-intuitive (there's only one intuitive interface, and it's got nothing to do with computers), it's that there are a wealth of "intuitive" meanings. A case can be made that it should mean the same as any of thise:

a = b.replace(c, '') a = b.replace(c, ' ', 1) a = b.replace(c, ' ')

For that matter, it might also mean the same thing as any of these:

a = re.sub(r'\s*%s\s*' % c, '', b, 1) a = re.sub(r'\s*%s\s*' % c, '', b) a = re.sub(r'\s*%s\s*' % c, ' ', b, 1) a = re.sub(r'\s*%s\s*' % c, ' ', b) a = re.sub(r'%s\s*' % c, '', b, 1) a = re.sub(r'%s\s*' % c, '', b) a = re.sub(r'%s\s*' % c, ' ', b, 1) a = re.sub(r'%s\s*' % c, ' ', b) a = re.sub(r'\s*%s' % c, '', b, 1) a = re.sub(r'\s*%s' % c, '', b) a = re.sub(r'\s*%s' % c, ' ', b, 1) a = re.sub(r'\s*%s' % c, ' ', b)

Unless you can make a clear case as to why exactly one of those cases is different enough from the others to warrant a syntax all it's own, It's probably best to be explicit about the desired behavior.

 <mike

-- Mike Meyer <mwm at mired.org> http://www.mired.org/consulting.html Independent Network/Unix/Perforce consultant, email for more information.

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