What does `int` parameter in `map` function of Python 3?

Question

if __name__ == '__main__':
n = int(input())
arr = map(int, input().split())

In the above code, map function taking two parameters, I got the understanding of the second parameter what it does but I am not getting 'int' parameter.

Have you read the documentation? Which part didn't you understand? — Aran-Fey, Jul 29 '18 at 18:03
[Are you for real?](https://docs.python.org/3/library/functions.html#int) — Ignacio Vazquez-Abrams, Jul 29 '18 at 18:04
Yes, I had read the documentation and many more other resources but I am not getting 'int' parameter in the map function. What is the use of this? @Aran-Fey — Prathamesh More, Jul 29 '18 at 18:13
@IgnacioVazquez-Abrams Thank you for doc link. I got some idea! — Prathamesh More, Jul 29 '18 at 18:15

Ectras · Answer 1 · 2020-10-20T16:01:23.883

4

map(function, iterable) Return an iterator that applies function to every item of iterable, yielding the results.
int(x) Return an integer object constructed from a number or string x.

Therefore, it will return an iterable where it applied the int() function to each substring from .split(), meaning it casts every substring to int.

Example:

arr = map(int, "12 34 56".split())
arr = list(arr) # to convert the iterable to a list
print(arr) # prints: [12, 34, 56]

# This is equivalent:
arr = [int("12"), int("34"), int("56")]

Other example with custom function instead of int():

def increment(x):
    return x + 1

arr = map(increment, [1, 2, 3, 4, 5])
arr = list(arr)
print(arr) # prints: [2, 3, 4, 5, 6]

edited Oct 20 '20 at 16:01

answered Jul 29 '18 at 18:24

Ectras

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4

Oh! This string will be converted to integer! – Prathamesh More Jul 29 '18 at 18:29
2

split breaks it up and int converts each bit to integers, yes. – Zev Jul 29 '18 at 18:31

Zev · Accepted Answer · 2018-07-29T18:30:22.253

3

Let's say I type 5 and then enter at the first prompt:

n = int(input())

Would take the input "5" and make it into the integer 5. So we are going from a string to an int

Then we will get another input prompt because we have input() again in the next line: This time I'll type 123 324 541 123 134 and then enter.

the .split() will split this into "123", "324", "541", "123", "134" which is a list (well a map) of strings. Then we'll map int onto them to give ourselves a map of ints rather than strings. int converts the strings to integers.

When checking out code it is often helpful to try things in a REPL (read execute print, looper). In your command promt just type python or python3 if you have it installed or use replt.it. Type a = "123" + "321" then try `a = int("123") + int("321")

Wrap this with list(map(int, input().split())) to get a list rather than a map.

edited Jul 29 '18 at 18:30

answered Jul 29 '18 at 18:17

Zev

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That's a perfect explanation! Now, How can I access the first element of arr list? @Zev – Prathamesh More Jul 29 '18 at 18:21
When I try to access the first element of arr list. I getting an error. ~if __name__ == '__main__': n = int(input()) arr = map(int, input().split()) save = 0; smallNumber = arr[0]~ – Prathamesh More Jul 29 '18 at 18:23
`arr[0]` is not working. `smallNumber = arr[0] TypeError: 'map' object is not subscriptable` – Prathamesh More Jul 29 '18 at 18:25
see my edit. You need `list()` around it so it isn't a map but a list. – Zev Jul 29 '18 at 18:26
Oh! Got it! Thank you! – Prathamesh More Jul 29 '18 at 18:27

What does `int` parameter in `map` function of Python 3?

2 Answers2