Fixed point arithmetic library fro Python. I developed this to aid me in studying Circuit perspective of Computer Arithmetic.

fixed_point.py

def bin_complement(a):
  tmpBin = list(a)
  for i, c in enumerate(tmpBin):
    if c == "1":
      tmpBin[i] = "0"
    else:
      tmpBin[i] = "1"
  return ''.join(tmpBin)
  
def bin_increment(a):
  tmpBin = list(a)
  for i, c in enumerate(tmpBin[::-1]):
    if c == "0":
      tmpBin[-i-1] = "1"
      break
    else:
      tmpBin[-i-1] = "0"
  return ''.join(tmpBin)

class FixedPoint:
  _data = "" # actual data
  _significant_width = 0 # Width of significant part
  _fraction_width = 0 # Width of part
  
  def __init__(self, significant_width, fraction_width):
    self._significant_width = significant_width
    self._fraction_width = fraction_width
    
  def total_width(self):
    return self._significant_width + self._fraction_width
    
  def get_number(self):
    tStr = self._data
    tData = 0.0
    neg = tStr[0] == "1"
    
    if neg:
      tStr = bin_complement(tStr)
      tStr = bin_increment(tStr)
    
    for i, c in enumerate(tStr[::-1]):
      if c == "1":
        pow_val = i - self._fraction_width
        tData = tData + (2**pow_val)
    if neg:
      tData = -tData
    
    return tData
  
  def _dec2bin(self, dec, tot_width):
    tStr = bin(dec & int("1" * tot_width, 2))[2:]
    tStr = ("0" * (tot_width - len(tStr))) + tStr
    return tStr
  
  def get_binary_string(self):
    return self._data
  
  # print the fixed point number in binary with a binary point
  def print_bin(self):
    data = self._data
    data_str = "0"
    if self._significant_width > 0:
      data_str = data[:self._significant_width]
      
    if self._fraction_width > 0:
      data_str = data_str + '.' + data[-self._fraction_width:]

    print data_str
  
  def from_number(self, data):
    #Python doesn't allow float to binary conversion
    
    #We multiply the data with 2^fraction_part and convert it to int
    #Now we can use built in format function on int to convert to binary
    tData = int(data * (2**self._fraction_width))
    #We only need total_width number of binary bits
    data_str = self._dec2bin(tData, self.total_width())
    
    self._data = data_str
    return True
  
  def from_binary_str(self, data):
    if len(data) != self.total_width():
      return False
    self._data = data
    return True
    
  #operators
  
  #Addition operator
  def __add__(self, other):
    if isinstance(other, FixedPoint):
      return self.get_number() + other.get_number()
    elif isinstance(other, int) or isinstance(other, float):
      return self.get_number() + other
    else:
      return 0
      
  def __radd__(self, other):
    if isinstance(other, FixedPoint):
      return self.get_number() + other.get_number()
    elif isinstance(other, int) or isinstance(other, float):
      return self.get_number() + other
    else:
      return 0
      
  def __sub__(self, other):
    if isinstance(other, FixedPoint):
      return self.get_number() - other.get_number()
    elif isinstance(other, int) or isinstance(other, float):
      return self.get_number() - other
    else:
      return 0
      
  def __rsub__(self, other):
    if isinstance(other, FixedPoint):
      return self.get_number() - other.get_number()
    elif isinstance(other, int) or isinstance(other, float):
      return other - self.get_number()
    else:
      return 0
      
  def __mul__(self, other):
    if isinstance(other, FixedPoint):
      return self.get_number() * other.get_number()
    elif isinstance(other, int) or isinstance(other, float):
      return self.get_number() * other
    else:
      return 0
      
  def __rmul__(self, other):
    if isinstance(other, FixedPoint):
      return self.get_number() * other.get_number()
    elif isinstance(other, int) or isinstance(other, float):
      return self.get_number() * other
    else:
      return 0