how to map over a function with multiple arguments in python

Question

I'm looking to map over a function with lists for specific arguments.

def add(x, y):
    return(x + y)

list1 = [1, 2, 3]
list2 = [3, 4, 5]

After some research I have been able to successfully do it using map and a lambda function.

list(map(lambda x, y: add(x, y), list1, list2))

I was wondering, is it better to do this using an iterator? I tried the following but couldn't figure it out:

[add(x, y), for x, y in list1, list2]

or

[add(x, y), for x in list1 for y in list2]

Thanks in advance!

Use zip for a list comprehsion

juanpa.arrivillaga
– juanpa.arrivillaga

2017-12-17 20:41:02 +00:00
Commented Dec 17, 2017 at 20:41 — juanpa.arrivillaga
– juanpa.arrivillaga, Commented Dec 17, 2017 at 20:41

willeM_ Van Onsem · Accepted Answer · 2017-12-17 20:43:55Z

18

There is no need to use a lambda expression here, you can pass a reference to te function directly:

list(map(add, list1, list2))

In case you want to use list comprehension, you can use zip:

[add(x, y) for x, y in zip(list1, list2)]

zip takes n iterables, and generate n-tuples where the i-th tuple contains the i-th element of every iterable.

In case you want to add a default value to some parameters, you can use partial from functools. For instance if you define a:

def add (x, y, a, b):
    return x + y + a + b

from functools import partial

list(map(partial(add, a=3, b=4), list1, list2))

Here x and y are thus called as unnamed parameters, and a and b are by partial added as named parameters.

Or with list comprehension:

[add(x, y, 3, 4) for x, y in zip(list1, list2)]

edited Dec 17, 2017 at 20:43

answered Dec 17, 2017 at 20:39

willeM_ Van Onsem

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4 Comments

Matt W. Over a year ago

ok, awesome. what if there were a couple other arguments that didn't change. like add(a, b, x, y), and you want to set a = 3, b = 4, and then iterate through the lists for x and y?

Matt W. Over a year ago

your edit answered my above Q. Also, it threw an error I think because of the comma you have after add(x, y),. Once I removed that it worked.

willeM_ Van Onsem Over a year ago

@MattW.: indeed, thanks for spotting it, removed it now :)

Matt W. Over a year ago

Thanks for your answer! fixed my issue, and was a great explanation. I'll accept as soon as SO lets me. cheers

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