Monday, December 6, 2010

string substitution in list

While coding the other day ... I came across this suspiciously looking code that almost look like it would work ...

substituted = ["My name is %s","My name is %s", "My name is %s" ] % ["Earl","Matthew","David"]

So used to looking at string substitution, I almost thought that code could work ... of course in order for that to work correctly ... it would have to be something like this ...

strings = ["My name is %s","My name is %s", "My name is %s" ]
names = ["Earl","Matthew","David"]
substituted = [ string % name for string,name in zip(strings,names) ]

It's string substitution and list substitution .. Repeat that 10 times :). It's always good and enlightening to strip right down to the basics most days. Go on run the first part of the code and see what you get.


Anonymous said...

It's "list comprehension", which is even more fun to say. I don't think I've ever seen "list substitution" used anywhere.

lowks said...

Marius: I guess I can call it ... string substitution via list comprehension.

alex dante said...

class TemplateList(list):
def __mod__(self, other):
return [s % v for (s, v) in zip(self, other)]

>>> substituted = TemplateList(['My name is %s'] * 3) % ['Earl', 'Matthew', 'David']
>>> print substituted
['My name is Earl', 'My name is Matthew', 'My name is David']


(Sorry, the lack of pre tags makes that look godawful...)

lowks said...

Alex: Bravo!

Frank said...

['My name is %s' % name for name in ['Earl', 'Matthew', 'David']]

More concise I think.