Question

This is quite n00bish, but I’m trying to learn/understand functional programming in python. The following code:

foos = [1.0,2.0,3.0,4.0,5.0] bars = [1,2,3]  def maptest(foo, bar):     print foo, bar  map(maptest, foos, bars) 

produces:

1.0 1 2.0 2 3.0 3 4.0 None 5.0 None 

Q. Is there a way to use map or any other functional tools in python to produce the following without loops etc.

1.0 [1,2,3] 2.0 [1,2,3] 3.0 [1,2,3] 4.0 [1,2,3] 5.0 [1,2,3] 

Just as a side note how would the implementation change if there is a dependency between foo and bar. e.g.

foos = [1.0,2.0,3.0,4.0,5.0] bars = [1,2,3,4,5] 

and print:

1.0 [2,3,4,5] 2.0 [1,3,4,5] 3.0 [1,2,4,5] ... 

P.S: I know how to do it naively using if, loops and/or generators, but I’d like to learn how to achieve the same using functional tools. Is it just a case of adding an if statement to maptest or apply another filter map to bars internally within maptest?

Answer 1

The easiest way would be not to pass bars through the different functions, but to access it directly from maptest:

foos = [1.0,2.0,3.0,4.0,5.0] bars = [1,2,3]  def maptest(foo):     print foo, bars  map(maptest, foos) 

With your original maptest function you could also use a lambda function in map:

map((lambda foo: maptest(foo, bars)), foos)