If you want to round the value, do:

str(int(f+0.5))

If you want to truncate the value, do:

str(int(f))

>>> str(42)
'42'

>>> int('42')
42

Links to the documentation:

• int()
• str()

str(x) converts any object x to a string by calling x.__str__(), or repr(x) if x doesn't have a __str__() method.

Refer to a basic atoi in C:

int myAtoi(char *str)
{
    int res = 0; // Initialize result

    // Iterate through all characters of input string and update result
    for (int i = 0; str[i] != '\0'; ++i)
        res = res*10 + str[i] - '0';

    // return result.
    return res;
}

Which translates into the Python:

def atoi(s):
    rtr=0
    for c in s:
        rtr=rtr*10 + ord(c) - ord('0')

    return rtr

Test it:

>>> atoi('123456789')
123456789   

If you want to accommodate an optional sign and whitespace the way that int does:

def atoi(s):
    rtr, sign=0, 1
    s=s.strip()
    if s[0] in '+-':
        sc, s=s[0], s[1:]
        if sc=='-':
            sign=-1

    for c in s:
        rtr=rtr*10 + ord(c) - ord('0')

    return sign*rtr

Now add exceptions and you are there!