Bigint multiply PoC | Python Fiddle

lhs = "1234728"
rhs = "38910"

def carry(l):
  output = []
  cval = 0
  for x in l[::-1]:
    v = x+cval
    output.insert(0,v%10)
    if v > 9:
      cval = v/10
    else:
      cval = 0
  while cval > 0:
    output.insert(0,cval%10)
    cval /= 10

return output

def add(l, r):
  if len(l) < len(r):
    while len(l) < len(r):
      l.insert(0,0)
  else:
    while len(r) < len(l):
      r.insert(0,0)

result = [0]*len(l)

for i in enumerate(l):
    i = i[0]
    result[i] = l[i] + r[i]

return carry(result)

def mult(l, r):
  isNegative = False
  # Yes there's a more elegant way to handle this
  # Thanks for asking
  if l[0] == "-": #Negative
    isNegative = True
    l = l[1:]
    if r[0] == "-":
      isNegative = False
      r = r[1:]
  elif r[0] == "-":
    isNegative = True
    r = r[1:]
  if len(l) < len(r):
    # Trivial loop optimization
    t = l
    r = l
    l = r
  results = []
  p = 0
  for c in r[::-1]: # Reverse iterate over the smaller number
    out = []
    for d in l[::-1]:
      out.insert(0,int(c)*int(d))
    out += [0] * p
    out = carry(out)
    results.append(out)
    p += 1

final = []

for x in results:
    final = add(final,x)

return ''.join([str(x) for x in final])

print mult(lhs, rhs)
print str(int(lhs)*int(rhs))

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