Python (Recursion): "TypeError: string indices must be integers" in Recursion

Question

Just started learning DS&A on my own recently and in the Recursion part of the book, it lists the code below as a basic example of Recursion being used to convert an integer into a string:

def to_str(n,base):
convert_string = "0123456789ABCDEF"
if n < base:
    return convert_string[n]
else:
    return to_str(n/base,base) + convert_string[n%base]

When I call the function and print using print(to_str(1453,10)), I get the error: TypeError: string indices must be integers.

What am I doing wrong?

Blckknght · Accepted Answer · 2018-10-04 04:53:22Z

1

In Python 3, the / operator always returns a float object, even if the two numbers you're dividing are both integers. If you want integer division, use the // operator instead:

return to_str(n // base, base) + convert_string[n % base]

answered Oct 4, 2018 at 4:53

Blckknght

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Comments

Ernest S Kirubakaran · Accepted Answer · 2018-10-04 04:55:16Z

0

You are getting this error because the value for n/base in the second return statement is a float. Just explicitly convert it to integer.

def to_str(n, base):
    if n < base:
        return convert_string[n]
    else:
        return to_str(int(n/base), base) + convert_string[n%base]

answered Oct 4, 2018 at 4:55

Ernest S Kirubakaran

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