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The usual way to input n numbers is to first ask for n and then type n numbers in different lines.

n = int(input())
for i in range(n):
 x = int(input())

How can I ask for n and type the n numbers in only one line.

Something like this:

>> 4 1 2 3 4

How can I ask for n and type the n numbers in only one line.

You don't need to ask for n if it's obvious from the whitespace-separated input how many integers you have.

However, if the input string format is non-negotiable, you can split via sequence unpacking:

n, *num_list = map(int, input().split())

For example, with input '4 1 2 3 4', you will have the following result:

print(n, num_list)

4 [1, 2, 3, 4]

To understand the above logic:

1. 
   input().split() splits a string input by whitespace into a list.


2. 
   map(int, X) returns an iterable of int applied to each element in X.


3. 
   n, *num_list = map(...) iterates the map object and separates into the first and the rest.

More idiomatic would be to calculate n yourself:

num_list = list(map(int, input().split()))
n = len(num_list)

For example, with input '1 2 3 4', you will have the following result:

print(n, num_list)

4 [1, 2, 3, 4]

The only purpose of entering the number of numbers explicitly is to provide a check. This is possible via an assert statement:

n, *num_list = map(int, input().split())

assert n == len(num_list), f'Check failed: n vs len(num_list) provided does not match'

Perhaps you can try processing the entire input as a string. Then convert them to integers. In that case, you won't need to specify the value of n too.

>>> x = [int(y) for y in input().split()]
1 2 3 4
>>> x
[1, 2, 3, 4]

You can then work with the values by iterating through the list. If you need the value of n, just get the length of the list.

>>> n = len(x)
>>> n
4

space_separated_numbers = input()
num_list = [int(x) for x in space_separated_numbers.split()]

The trick is to take the whole input as a string at once, and then split it yourself.

EDIT: If you are only concerned with getting the first number, just get the first value instead.

space_separated_numbers = input()
num = space_separated_numbers.split()[0]