float_int.py

# Function recreating the functionality of float() and int() in Python.
# By Neil Fraser.  Public Domain.  2012.

def myFloat(input = 0.0):
  if type(input) != str:
    if type(input) == bool:
      return input and 1.0 or 0.0
    if type(input) == float:
      return input
    if type(input) in (int, long):
      return input + 0.0
    raise(TypeError('myFloat() argument must be a string or a number'))

  # Leading/trailing whitespace is ignored.  Normalize to uppercase.
  input = input.strip().upper()

  # No known way to generate inf or nan without using float().
  if input in ('INF', 'INFINITY', '+INF', '+INFINITY'):
    raise(NotImplementedError('myFloat() can\'t generate infinity'))
  elif input in ('-INF', '-INFINITY'):
    raise(NotImplementedError('myFloat() can\'t generate -infinity'))
  elif input in ('NAN', '+NAN', '-NAN'):
    raise(NotImplementedError('myFloat() can\'t generate NaN'))

  # Tokenize the input.
  negative = False
  integer = ''
  decimal = ''
  exp_negative = False
  exp_integer = ''
  # For maximum efficiency we should only store pointers to the start and end
  # positions of integer, decimal, and exp_integer, then slice them out in one
  # operation.  However, for simplicity we'll just accumulate them character
  # by character as strings.

  state = -1
  # Parse the input string with a finite state machine.
  # -1: Reading sign.
  #  0: Reading integer.
  #  1: Reading decimal.
  #  2: Reading exponent sign.
  #  3: Reading exponent.
  for c in input:
    if state == -1:
      state = 0
      if c == '-':
        negative = True
        continue
      elif c == '+':
        continue
      # No sign; fall through to state 0.
    if state == 0:
      if c.isdigit():
        integer += c
      elif c == '.':
        state = 1
      elif c == 'E':
        state = 2
      else:
        raise(ValueError('invalid integer for myFloat(): ' + input))
    elif state == 1:
      if c.isdigit():
        decimal += c
      elif c =='E':
        state = 2
      else:
        raise(ValueError('invalid decimal for myFloat(): ' + input))
    elif state == 2:
      if c == '+':
        state = 3
      elif c == '-':
        exp_negative = True
        state = 3
      elif c.isdigit():
        exp_integer = c
        state = 3
      else:
        raise(ValueError('invalid exponent for myFloat(): ' + input))
    elif state == 3:
      if c.isdigit():
        exp_integer += c
      else:
        raise(ValueError('invalid exponent integer for myFloat(): ' + input))
  
  if (not (integer or decimal) or (state >= 2 and not exp_integer)):
    raise(ValueError('could not convert string to float: ' + input))

  result = 0.0
  if integer:
    result = myInt(integer) + 0.0
  if decimal:
    decimal = myInt(decimal) / 10.0 ** len(decimal)
    result += decimal

  if exp_integer:
    exponent = myInt(exp_integer)
    if exp_negative:
      result /= 10 ** exponent
    else:
      result *= 10 ** exponent

  if negative:
    result = -result
  return result


def myInt(input = 0, *args):
  if len(args) > 1:
    raise(TypeError('int() takes at most 2 arguments (' +
                    str(len(args) + 1) + ' given)'))
  if len(args) == 1:
    base = args[0]
    if type(base) == bool:
      base = base and 1 or 0
    if type(base) == float:
      raise(TypeError('integer argument expected, got float'))
    if type(base) != int:
      raise(TypeError('an integer is required'))
    if type(input) != str:
      raise(TypeError('myInt() can\'t convert non-string with explicit base'))
    if base != 0 and (base < 2 or base > 36):
      raise(ValueError('myInt() base must be >= 2 and <= 36'))
  else:
    base = 10
  orig_base = str(base)

  if type(input) == int:
    return input
  if type(input) == bool:
    return input and 1 or 0
  if type(input) == long:
    input = str(input)
  if type(input) == float:
    # Remove the float's decimal.
    input = str(input)
    input = input[:input.index('.')]
  if type(input) != str:
    raise(TypeError('myInt() argument must be a string or a number, ' +
                    'not \'' + str(type(input)) + '\''))

  # Leading/trailing whitespace is ignored.  Normalize to uppercase.
  input = input.strip()
  orig_input = input
  input = input.upper()

  # Handle any leading sign.
  negative = False
  if input.startswith('-'):
    negative = True
    input = input[1:]
  elif input.startswith('+'):
    input = input[1:]
  if not input:
    raise(ValueError('empty literal for myInt()'))

  # Determine assumed base.
  if base == 0:
    if input.startswith('0B'):
      base = 2
      input = input[2:]
    elif input.startswith('0X'):
      base = 16
      input = input[2:]
    elif input.startswith('0O'):
      base = 8
      input = input[2:]
    elif input.startswith('0'):
      base = 8
      input = input[1:]
    else:
      base = 10

  integer = 0
  multiplier = 1
  for c in range(len(input) - 1, -1, -1):
    n = ord(input[c])
    if 48 <= n <= 57:  # 0-9
      n -= 48
    elif 65 <= n <= 90:  # A-Z
      n -= (65 - 10)
    else:
      n = 99
    if n >= base:
      raise(ValueError('invalid literal for myInt() with base ' + orig_base +
                       ': \'' + orig_input + '\''))
    integer += n * multiplier
    multiplier *= base

  if negative:
    integer = -integer
  return integer