How To Split The Integers And Operators Characters From String In Python?

I want to split the string into integers and operators for doing Infix expression evaluation in python. Here is my string: >>> s = (1-2+3)*5+10/2 I tried this to split: &

Solution 1:

This is not the best solution for infix. Remove the + after [] like:

import re
s = "(1-2+3)*5+10/2"print re.findall('[+-/*//()]|\d+',s)

['(', '1', '-', '2', '+', '3', ')', '*', '5', '+', '10', '/', '2']

Try the following link for correct solution: Simple Balanced Parentheses

from pythonds.basic.stack import Stack

defpostfixEval(postfixExpr):
    operandStack = Stack()
    tokenList = postfixExpr.split()

    for token in tokenList:
        if token in"0123456789":
            operandStack.push(int(token))
        else:
            operand2 = operandStack.pop()
            operand1 = operandStack.pop()
            result = doMath(token,operand1,operand2)
            operandStack.push(result)
    return operandStack.pop()

defdoMath(op, op1, op2):
    if op == "*":
        return op1 * op2
    elif op == "/":
        return op1 / op2
    elif op == "+":
        return op1 + op2
    else:
        return op1 - op2

print(postfixEval('7 8 + 3 2 + /'))

Keep in mind that this is a postfix implementation and its just for example. Do the infix by yourself and if you have any difficulties just ask.

Solution 2:

Try

re.findall('[+-/*//()]|\d+',s)

You don't need the +, since you only want to have one special sign.

Solution 3:

Using split:

printfilter(lambda x: x, re.split(r'([-+*/()])|\s+', s))

Solution 4:

If you can avoid regular expressions, you can try an iterative solution (just a rough code):

s = "(1-2+3)*5+10/2"
numbers = "0123456789."

def split_operators(s):
    l = []
    last_number = ""for c in s:
        if c in numbers:
            last_number += c
        else:
            if last_number:
                l.append(last_number)
                last_number = ""if c:
                l.append(c)
    if last_number:
        l.append(last_number)
    return l

print split_operators(s)

result:

['(', '1', '-', '2', '+', '3', ')', '*', '5', '+', '10', '/', '2']