Implementation of atoi

__init__.py

''' atoi package '''

atoi.py

''' atoi converts string representations of integers and floats to their numeric type
'''

from decimal import Decimal

ORD_0 = ord('0')


def atoi_int(s):
    ''' atoi_int converts a string representation of an integer into an integer

    Args:
        s (str): string representing an integer

    Returns:
        int: integer equivalent of `s`
    '''
    sum = 0
    s_len = len(s)
    for i in range(s_len):
        sum += (ord(s[s_len-(i+1)]) - ORD_0) * (10 ** i)
    return sum


def atoi_float(s):
    ''' atoi_float converts a string representation of a float to a float
        Note: uses the `decimal` package because the floating point byte conversion produce results
            that are unexpected. Example: 3.14159 == 3.14159000000000002

    Args:
        s (str): string representing a floating point number

    Return:
        float: floating point equivalent
    '''
    if '.' in s:
        d, f = s.split('.', 1)
    else:
        d = s
        f = '0'

    sum = Decimal(0)
    f_len = len(f)

    for i in range(f_len):
        sum += Decimal(ord(f[i]) - ORD_0) / (10 ** (i+1))

    return float(atoi_int(d) + sum)

test_atoi.py

''' test_atoi includes nosetests for atoi functions

    to run:
        `# nosetests -v`
'''
from .atoi import atoi_int, atoi_float


def test_int():
    cases = (
        ('1234', 1234),
        ('42', 42),
        ('8675309', 8675309),
        ('5150', 5150),
    )
    for s, want in cases:
        got = atoi_int(s)
        assert want == got, 'integer mismatch - want: {0}, got: {1}'.format(want, got)


def test_float():
    cases = (
        ('1234.5678', 1234.5678),
        ('3.14159', 3.14159),
        ('1.6180', 1.618),
        ('0', 0.0),
        ('21', 21.0),
        ('0.739085', 0.739085),
    )
    for s, want in cases:
        got = atoi_float(s)
        assert want == got, 'float mismatch - want: {0}, got: {1}'.format(want, got)