Print function in Python 3 isn't adding but appending?

Question

I am a C programmer with a decent knowledge of C++. I am learning python and was trying some stuff with the new syntax.

a=input("a: ")
b=input("b: ")

print("a+b=", 2*a + b)

Say I enter a=10 and b=20. Very strangely, this gives an output of 101020.

Why is this happening?

`int(input("a: "))` should get you what you want. It's more like parsing an integer than type-casting — rdas, Jul 07 '20 at 05:31
@WilliamR.Ebenezer it's best not to think in terms of "type-casts" which imply certain low-level ideas which aren't really relevant in Python. You create int objects from string objects. But `str` objects support the `*` operator where it means "repitition", so `'abc'*3 == 'abcabcabc'` — juanpa.arrivillaga, Jul 07 '20 at 06:39

score 4 · Accepted Answer · answered Jul 07 '20 at 05:28

4

The type for the return of input() is string. 2*string simply copies the string twice. Hence the two tens followed by twenty all concatenated together.

answered Jul 07 '20 at 05:28

Cresht

1,020
2
6
15

score 2 · Answer 2 · answered Jul 07 '20 at 05:30

2

What you can do is you can wrap the inputs around the built-in int() function. This is the same as static casting in C++, since you said you're familiar with it.

This would be the most effective way to achieve what you're aiming for:

a=int(input("a: "))
b=int(input("b: "))
print("a+b=", 2*a + b)

This way, it no longer concatenates the two strings together but adds the newly converted integers.

answered Jul 07 '20 at 05:30

coddingtonjoel

189
2
12

Makes sense. Thanks. – William R. Ebenezer Jul 07 '20 at 05:31

Print function in Python 3 isn't adding but appending?

2 Answers2