for in loop arithmetic

Question

operation = ['/','*','+','-']
a =5
b= 2
for op in operation:
    output = a+op+b
    print output

Here the output I get is

5/2
5*2
5+2
5-2

but I want

What is the way to do it?

Why on earth would you expect e.g. `"5" + "/" + "2"` to be `2.5`? It's just a string, it won't be magically evaluated as a calculation (not to mention that, in Python 2.x, that calculation evaluates to `2`). — jonrsharpe, Oct 29 '14 at 12:16

chepner · Accepted Answer · 2014-10-29T12:47:18.497

1

The easiest way is to use a dictionary that maps the symbols to functions that perform the operation, which can be found in the operator module.

import operator
d = { '+': operator.add, '-': operator.sub, '*': operator.mul, '/': operator.div }
operation = d.keys()
a = 5
b = 2
for op in operation:
    output = d[op](a, b)
    print output

edited Oct 29 '14 at 12:47

answered Oct 29 '14 at 12:12

chepner

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score 1 · Answer 2 · answered Oct 29 '14 at 12:12

1

Use the operator module:

a, b = 5, 2
for op in (operator.div, operator.mul, operator.add, operator.sub):
    print(op(a, b))

answered Oct 29 '14 at 12:12

Fred Foo

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score 0 · Answer 3 · answered Oct 29 '14 at 12:11

For this you can use the eval function:

print eval(output)

Note: eval evaluates anything in the string, even if its dangerous. Also, as you know your operators in advance, you can use the operators module:

import operators
operation = [operators.div, operators.mul, operators.add, operators.sub]
a = 5
b = 2
for op in operation:
    output = op(a, b)
    print output

for in loop arithmetic

3 Answers3