Calculette Python by Yarflam

#!/usr/bin/python
# Calculette v1.0 by Yarflam

def calc(exp):
 r=''
 i=0
 while i < len(exp):
  if exp[i]=='P' and exp[(i+1)]=='I':
   r="3.1415926535897932384626433832795"
  if exp[i] in '0123456789.':
   r=r+exp[i]
  if exp[i]=='+':
   r=str(float(r)+calc(exp[(i+1):len(exp)]))
   break
  if exp[i]=='-':
   r=str(float(r)-calc(exp[(i+1):len(exp)]))
   break
  if exp[i]=='*':
   endx=exp.find('+',i) if (not exp.find('+',i) == -1) else len(exp)
   endx=exp.find('-',i) if (not exp.find('-',i) == -1) and (exp.find('-',i) < endx) else endx
   endx=calc_prio(exp) if (exp[(i+1)] == '(') else endx
   i=i+1 if (exp[(i+1)] == '(') else i
   r=str(float(r)*calc(exp[(i+1):endx]))
   i=(endx-1)
  if exp[i]=='/':
   endx=exp.find('+',i) if (not exp.find('+',i) == -1) else len(exp)
   endx=exp.find('-',i) if (not exp.find('-',i) == -1) and (exp.find('-',i) < endx) else endx
   endx=calc_prio(exp) if (exp[(i+1)] == '(') else endx
   i=i+1 if (exp[(i+1)] == '(') else i
   r=str(float(r)/calc(exp[(i+1):endx]))
   i=(endx-1)
  if exp[i]=='(':
   r=str(calc(exp[(i+1):calc_prio(exp)]))
   exp=exp[calc_prio(exp)+1:len(exp)]
   i=-1
  i=i+1
 return float(r)

def calc_prio(exp):
 cmpp=exp.count('(',0)
 l=-1
 mx=-1
 i=0
 while i < len(exp) and (l >= 0 or mx < 0):
  l=l+1 if exp[i]=='(' else l
  l=l-1 if exp[i]==')' else l
  mx=l if l > mx else mx
  i=i+1
 return (i-1)

c=raw_input('CALC: ')
print "= ",calc(c)
raw_input()