Base conversion algorithms in python

Ascii to Integer

Input - '123'

Output - 123

def atoi(s):

  res = 0

  for i in range(len(s)):

    n = ord(s[i]) - ord('0')

    res = res * 10 + n

  return res

Integer to ASCII

Input - 123

Output - '123'

def itoa(num):

  res = ""

  while num:

    n = num % 10

    res += chr(ord(str(n))) or res += str(n)

    num = num / 10

  return res[::-1]

Decimal to binary
Input - 5

Output - 101

def decimal_to_binary(num):

  res = ""

  while num:

    #even number and has 0

    if not num % 2:

      res += '0'

    else:

      res += '1'

    num = num / 2

  return res[::-1]

Binary to decimal

Input - 101

Output - 5

def binary_to_decimal(binary_str):

  res, shift = 0, 0

  for i in range(len(binary_str)-1, -1, -1):

        if int(binary_str[i]):

          res += (1 << shift)

        shift += 1

  return res

Hexadecimal to decimal 

Input - 7ED

Output - 2029

HEX_DEC = {'0':0, '1':1, '2':2, '3':3, '4':4, '5':5, '6':6, '7':7, '8':8, '9':9, 'A':10, 'B':11, 'C':12, 'D':13, 'E':14, 'F':15}

def hex_to_decimal(hex_str):

  index, res = 0, 0

  for i in range(len(hex_str)-1, -1, -1):

    res += HEX_DEC[hex_str[i]] * (16 ** index)

    index += 1

  return res

Deciaml to Hexadecimal 

Input - 2029

Output - 7ED

DEC_HEX = {0:'0', 1:'1', 2:'2', 3:'3', 4:'4', 5:'5', 6:'6', 7:'7', 8:'8', 9:'9', 10:'A', 11:'B', 12:'C', 13:'D', 14:'E', 15:'F'}

def decimal_to_hex(dec_num):

  res = ""

  while dec_num:

    rem = dec_num % 16

    res += DEC_HEX[rem]

    dec_num = dec_num / 16

  return res[::-1