4 ms·

I guess my next question is then - why is anyone using filter/map instead of comprehensions or even generator expressions? Familiarity when coming from FP?

viraptor 10y ago
In my experience filter/map are used by people who just don't know about comprehensions, or are not used to having them available. It takes some time to start using them where properly.
clusmore 10y ago
Well, for one I believe they pre-date comprehensions. Having them as functions is also occasionally useful for partial application, e.g. from functools import partial to_strings = partial(map, str) # vs def to_strings(seq): return (str(elem) for elem in seq)
- m_mueller 10y ago
  I can see it together with partial, yes, that's when it can become a bit cleaner. Another reason why I use map is when I want to use multiprocessing or multithreading (with IO heavy functions). But on a fine grained level of code I find it really hurts readability compared to comprehensions.
- EvilTerran 10y ago
  Or this: def to_strings(seq): return map(str, seq) Generally, when the operation I'm applying to each element happens to already be a named function, I find "map(f, seq)" preferable to "(f(x) for x in seq)".
pmontra 10y ago
Coming from Ruby it's easier to use map, because it's what Ruby's standard library offers. However comprehensions are not that harder when one finally decides to understand how they work. Not as readable as map() IMHO. Example: Ruby [1, 2, 3].map {|x| x*x} # object.method(args) vs Python [x*x for x in [1, 2, 3]] where we have the function first, then the definition of the variable, then the data. This is the opposite of the object.method OO notation and using a variable before defining it is not what we usually do. But it's almost the usual mathematical notation "for i in set do f(i)" with the function at the beginning. Not a big deal. About a problem raised in a comment of the post (which is from 2009): this is Guido (2009) about the lack of tail call optimization in Python http://neopythonic.blogspot.it/2009/04/tail-recursion-elimination.html http://neopythonic.blogspot.it/2009/04/tail-recursion-elimin...

viraptor 10y ago

In my experience filter/map are used by people who just don't know about comprehensions, or are not used to having them available. It takes some time to start using them where properly.

clusmore 10y ago

Well, for one I believe they pre-date comprehensions. Having them as functions is also occasionally useful for partial application, e.g. from functools import partial to_strings = partial(map, str) # vs def to_strings(seq): return (str(elem) for elem in seq)

m_mueller 10y ago
I can see it together with partial, yes, that's when it can become a bit cleaner. Another reason why I use map is when I want to use multiprocessing or multithreading (with IO heavy functions). But on a fine grained level of code I find it really hurts readability compared to comprehensions.
EvilTerran 10y ago
Or this: def to_strings(seq): return map(str, seq) Generally, when the operation I'm applying to each element happens to already be a named function, I find "map(f, seq)" preferable to "(f(x) for x in seq)".

pmontra 10y ago

Coming from Ruby it's easier to use map, because it's what Ruby's standard library offers. However comprehensions are not that harder when one finally decides to understand how they work. Not as readable as map() IMHO. Example: Ruby [1, 2, 3].map {|x| x*x} # object.method(args) vs Python [x*x for x in [1, 2, 3]] where we have the function first, then the definition of the variable, then the data. This is the opposite of the object.method OO notation and using a variable before defining it is not what we usually do. But it's almost the usual mathematical notation "for i in set do f(i)" with the function at the beginning. Not a big deal. About a problem raised in a comment of the post (which is from 2009): this is Guido (2009) about the lack of tail call optimization in Python http://neopythonic.blogspot.it/2009/04/tail-recursion-elimination.html http://neopythonic.blogspot.it/2009/04/tail-recursion-elimin...