Using split on an input string

Question

I'm a beginner to Python 3 and when I try this code it works:

a = input('Enter three digits separated by space:')
b = a.split()
mylist = [int(i) for i in b]
print(mylist)

Output:

Enter three digits separated by space:2 3 4
[2, 3, 4]

However I get errors when I try this:

a = input('Enter three digits separated by space:')
b = a.split()
mylist = [int(i**2) for i in b]
print(mylist)

Error: TypeError: unsupported operand type(s) for ** or pow(): 'str' and 'int'

In fact this works as well:

list1 = [2,3,4]
mylist = [int(i**2) for i in list1]
print(mylist)

What am I doing wrong?

Green Cloak Guy · Accepted Answer · 2020-02-19 16:30:08Z

5

You might want to do exponentiation after converting to an int:

mylist = [int(i)**2 for i in list1]

You can't raise a string to a power (do you know what the square of the string "blah" is?), but you can raise a number to a power. So you need to convert the string to a number first.

Of course, a.split() returns a list of smaller strings derived from the original string, and you have to turn them into numbers yourself, but you already figured this out.

answered Feb 19, 2020 at 16:30

Green Cloak Guy

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1 Comment

sedavidw Over a year ago

It's worth nothing that in the OP's question, the second example works and they are asking about the difference. The hardcoded list1 is using integer inputs and that's the main difference compared to the input method. Which takes a string and splits it into a list of strings

pk786 · Accepted Answer · 2020-02-19 18:50:36Z

Error in your code: you are trying to raise power before converting it to int

int(i**2) 
#should be 
int(i)**2

Another approach, using map function.

Syntax: map(func, iterable)

In python, String is iterable which means you can iterate over it. For example:

for i in "hello":
   print(i)

#output will be: 
    h
    e
    l
    l
    o

Another simple concept before moving to map function: split() function will return the list.

print(type("hello".split()))
#output will be
<class 'list'>

Lets use map function to answer your question:

a = map(int, input('Enter three digits separated by space:').split())

mylist = [i**2 for i in a]
print(mylist)

Explanation:

The input() function will ask user to enter three numbers separated by space and that will be a string, now you can use split function over the string returned by input().
Here, split function will return a list.
Now, map function comes into the picture, it will take each element from the list returned at step 2 and map it to the function, in this case, it will map each element of the list to int.
Variable a is map object, and map object is iterable, so you can apply for loop or list comprehension(you used list comprehension) to get desired output

Aniket singh · Accepted Answer · 2020-02-19 17:39:46Z

-1

you have to give condition for split like " " suppose the input is 2 3 4 and you want to split it as 2,3,4. and also the input return value as str so you have to change it to int as follows then you can use **

 a = input('Enter three digits separated by space:')
 b = map(int,a.split(" "))
 mylist = [i**2 for i in b]

this will work for you..

edited Feb 19, 2020 at 17:39

answered Feb 19, 2020 at 16:48

Aniket singh

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1 Comment

sedavidw Over a year ago

If you change the OP's code to use this instead this would not solve the problem

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