Syntax error when casting string to int

Question

My code:

def digit_sum(n):
    result = 0
    s = str(n)
    for c in s:
        result += (int)c    # invalid syntax??????????
    return result

print digit_sum(1234)

Result:

    result += (int)c    # invalid syntax??????????
                   ^
SyntaxError: invalid syntax

The function is supposed to return the sum of each digit of the argument "n". Why do I get SyntaxError in the commented line? The variable c is of type string so it shouldn´t be an issue to apply a type cast to int.

In Python you **do not cast that way**. – Willem Van Onsem Feb 25 '17 at 21:27 — Willem Van Onsem, Feb 25 '17 at 21:27

Willem Van Onsem · Accepted Answer · 2017-02-25T21:47:51.957

7

In Python you do not cast that way. You use:

result += int(c)

Technically speaking this is not casting: you call the int(..) builtin function which takes as input the string and produces its equivalent as int. You do not cast in Python since it is a dynamically typed language.

Note that it is of course possible that c contains text that is not an integer. Like 'the number fifteen whohaa'. Of course int(..) cannot make sense out of that. In that case it will raise a ValueError. You can use try-except to handle these:

try:
    result += int(c)
except ValueError:
    # ... (do something to handle the error)
    pass

edited Feb 25 '17 at 21:47

answered Feb 25 '17 at 21:27

Willem Van Onsem

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This can also throw an exception if `c` can't be converted into an integer. It will throw a `ValueError`exception so if possible treat it with a try-except. – Gustavo Gomes Feb 25 '17 at 21:31
1

@Gugas: that is indeed a good suggestion. I've added that tho the answer. – Willem Van Onsem Feb 25 '17 at 21:34
sorry but it's an `except` not a `catch` to pair with the try. – Gustavo Gomes Feb 25 '17 at 21:38
@Gugas: yeah, some brainfreeze (or being buzzy with too many things at once). Thanks. – Willem Van Onsem Feb 25 '17 at 21:39

score 2 · Answer 2 · answered Feb 25 '17 at 21:27

2

In Python, you cast a string to an integer by using a function int().

    result += int(c)

answered Feb 25 '17 at 21:27

Rok Povsic

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score 0 · Answer 3 · edited Feb 25 '17 at 22:13

0

def digit_sum(n):
        numsum=[]
        add_up=str(n)
    for n in add_up[0: len(add_up)]:
        numsum.append(int(n))
    return sum(numsum)
print digit_sum(1234)

Basically, you need to cast string to integer using int(n)

edited Feb 25 '17 at 22:13

Umang Gupta

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answered Feb 25 '17 at 22:02

Melansia

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Syntax error when casting string to int

3 Answers3