Daniel Carrera a �crit :
Quinn Dunkan wrote:
Python has first class functions and lexical scoping, and encourages higher-order functions, though to a much lesser degree than a real functional language.
I was surprised to hear about first class functions and higher order functions. So I googled for a bit, and I found something neat:
---<snip>--- # Python implementation of Common Lisp's remove_if def remove_if(predicate, lst): return [elem for elem in lst if not predicate(elem)]
print remove_if(lambda x:x % 2, [1,2,3,4,5,6,7,8]) ---<snip>---
This is so cool. So there we have a higher order function, passing a funtion as an argument, and even lambda notation. Neat.
Well, I would not recommand using lambda functions ! The main reason is they are limited in that they only accept expressions (ie. not statements) and you can end up with very ugly things (mainly because of the lack of if-expressions).
Better use local functions for the same goal ! So your example becomes:
>>> def is_even(x): ... return x%2 >>> print remove_if(is_even, [1,2,3,4,5,6,7,8])
Or even better:
>>> def is_even(x): ... return x%2 >>> print remove_if(is_even, xrange(1,9))
And as local functions have lexical closure this is very interesting (much more than lambda).
It is very natural to write in a somewhat functional style, especially in regards to sequence processing: higher order functions and listcomps provide the processing and its built in generators and iterator protocol provide some of the benefits of laziness.
Hhhmmm.. I guess the above is also an example of that.
[snip: lots of very interesting info I didn't know about]
Thank you for all the information. I learned a lot today. I had no idea that Python had these features.
Cheers, Daniel. _______________________________________________ Haskell-Cafe mailing list [email protected] http://www.haskell.org/mailman/listinfo/haskell-cafe
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