CODEWITHSUNDEEP
pythonfunctionmathoperatorscalculator
user3327457
user3327457

Reputation:

Python - use an operator at runtime

Is it possible to insert an operation (e.g *, +) between two variables at runtime? My solution without doing this is multiple if, elif statements, but I don't think that's the most efficient way to do it.

EDIT: What I meant is I get two integers, and I want to apply an operation on one of them with the other, e.g x * y, but I want to change * to another operator (maybe they're called functions? Not sure) e.g -, +,^ based on input.

Does that make sense? Basically think of it as a calculator.

Upvotes: 2

Views: 280

Answers (4)

Rambo V
Rambo V

Reputation: 1

If your list of operators is small enough you can probably use lambdas.

def operator_factory(op):
    if op == '+':
        return lambda x,y: x + y
    elif op == '-':
        return lambda x,y: x - y
    elif op == '*':
        return lambda x,y: x * y
    elif op == '/':
        return lambda x,y: x / y
    elif op == '^':
        return lambda x,y: x ^ y

Your if statements can depend on user input. Then you just use this like so:

>>> f = operator_factory('+')
>>> f(2,3)
5

Upvotes: 0

Aaron Hall
Aaron Hall

Reputation: 395045

To answer the follow-on question, for example, you can subclass int and then implement __xor__ to exponentiate instead of apply a bitwise or, which is called by the ^ operator:

import operator

class MyInt(int):
    def __xor__(self, other):
        return operator.pow(self, other)

and then:

>>> i = MyInt(2)
>>> i
2
>>> type(i)
<class '__main__.MyInt'>
>>> j = 3
>>> i^j
8

Upvotes: 1

shx2
shx2

Reputation: 64318

@AaronHall's is the answer you're looking for, but for completeness, I'd mention you can also use eval.

var_1 = 2
var_2 = 3
op = '+'
print eval('%s%s%s' % (var_1, op, var_2))

However, eval is evil, so either don't use it, or use with caution.

Upvotes: 4

Aaron Hall
Aaron Hall

Reputation: 395045

I'm not sure if this is what you're looking for but the operator module has a lot of operations, e.g. add and mul (multiply):

import operator

var_1 = 2
var_2 = 3

print(operator.add(var_1, var_2))
print(operator.mul(var_1, var_2))

will print

5
6

Upvotes: 5

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