What is the problem with this simple code using map function in python?

Question

Code is as follows:

def func(i,j):
    return i+j

m = list(product(range(5),range(7)))
print(m)
x = map(func,m)
list(x)

Error :

[(0, 0), (0, 1), (0, 2), (0, 3), (0, 4), (0, 5), (0, 6), (1, 0), (1, 1), (1, 2), (1, 3), (1, 4), (1, 5), (1, 6), (2, 0), (2, 1), (2, 2), (2, 3), (2, 4), (2, 5), (2, 6), (3, 0), (3, 1), (3, 2), (3, 3), (3, 4), (3, 5), (3, 6), (4, 0), (4, 1), (4, 2), (4, 3), (4, 4), (4, 5), (4, 6)]
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-181-fdda131ed5e8> in <module>()



      5 print(m)
      6 x = map(func,m)
----> 7 list(x)

TypeError: func() missing 1 required positional argument: 'j'

How to pass each pair in m through func. I don't want any for loop.

posible duplicate stackoverflow.com/questions/10834960/…

Basalex
– Basalex

2019-11-29 14:23:42 +00:00
Commented Nov 29, 2019 at 14:23 — Basalex
– Basalex, Commented Nov 29, 2019 at 14:23

javidcf · Accepted Answer · 2019-11-29 14:20:07Z

2

You can use itertools.starmap:

from itertools import product, starmap

def func(i,j):
    return i+j

m = list(product(range(5),range(7)))
print(m)
x = starmap(func,m)
list(x)

answered Nov 29, 2019 at 14:20

javidcf

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4 Comments

Jon Clements Over a year ago

Ahh... I'd forgotten about starmap... although result = [func(*el) for el in m] is readable enough

javidcf Over a year ago

@JonClements @chepner Yes, in most cases I probably wouldn't use starmap personally (I rarely use map), but I had the impression OP wanted something without a for (but maybe they just don't want proper loops but and are okay with comprehension/generator).

Jon Clements Over a year ago

@chepner for 2-arg calls yeah... doesn't hurt to unpack it, but I'd probably not continue that pattern where there's more arguments...

Jon Clements Over a year ago

@chepner ... or there was a need to re-order or otherwise manipulate the arguments before passing to the function

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