How to solve expressions from a list?-CodePudding

I have a list of expressions ( - *): ["2 3", "5 - 1", "3 * 4", ...] and I need to convert every expresion to expression = answer like this 2 3 = 5.

I tried just doing print(listt[0]) but it outputs 2 3, not 5. So how do i get the answer of this expression? I know that there is a long way by doing .split() with every expression, but is there any other faster way of doing this?

UPD: I need to use only built-in functions

CodePudding user response：

You can use the eval() function from Python Builtins :

for expr in yourlist:
    print(expr, "=", eval(expr))
    # 2 3 = 5

As stated in the comments, this is not malicious-proof. Use this only if you know the string being evaluated are indeed simple arithmetic expressions.

CodePudding user response：

If you want to avoid using eval() (and you probably should) then you could do something like this:

from operator import add, sub, mul, truediv
from re import compile

OMAP = {
    ' ': add,
    '-': sub,
    '*': mul,
    '/': truediv
}

pattern = compile(r'^(\d \.*\d*)\s*(.)\s*(\d \.*\d*)$')

exprs = ["2   3.5", "5 - 1", "3 * 4", "3 / 4"]

def convert(s):
    try:
        return int(s)
    except ValueError:
        pass
    return float(s)

for expr in exprs:
    x, o, y = pattern.findall(expr)[0]
    r = OMAP[o](convert(x), convert(y))
    print(f'{expr} = {r}')

Output:

2   3 = 5.5
5 - 1 = 4
3 * 4 = 12
3 / 4 = 0.75

Note:

This is not robust as it assumes that the operators are only ever going to be one of , -, *, / and furthermore that the pattern always matches the regular expression.

Input data changed to include a floating point number