Use a string (representing a logical operator) in a Python expression

Question

Is it possible to somehow cast a string of, say, or or and into a form that is recognizable as a logical operator?

For example, is it possible to do something like this:

l = [1, 2, 3, 4, 5]
o = {item1:'or'}

for i in l:
    if i > 4 o[item1] i < 0:
        print i

where o[item1] is recognized as a valid or logical operator?

It is possible to create an equivalent equivalent (fsvo) expression, but it is not possible to use it like that - which is merely invalid syntax - and the expression itself needs to be altered. — user2864740
– user2864740, Commented Sep 10, 2014 at 20:08
With some trickery you could get an (i > 4) |o[item1]| (i < 0) syntax to work (without short-circuiting) but you'd never use that in any real code so it's not much more than a parlour trick. Is there a particular problem you think this would help with? Maybe there's a better way to solve it. — DSM
– DSM, Commented Sep 10, 2014 at 20:20
I'm trying to solve the question I posted here: stackoverflow.com/questions/25691990/… — Ryan
– Ryan, Commented Sep 10, 2014 at 20:23
@DSM: and you could actually use a lot of different delimiters, like a <o[x]> b or a **o[x]** b or even a %o[x]% b...the possibilities are endless! :P — nneonneo
– nneonneo, Commented Sep 10, 2014 at 20:23

nneonneo · Accepted Answer · 2014-09-10 20:07:17Z

5

You may use the operator package:

import operator

o = {item1: operator.or_}

if o[item1](i>4, i<0):
    ...

Note that or_ does not short-circuit, like or does. If you really need the short-circuit behaviour, you can use eval (but this is in general not recommended).

answered Sep 10, 2014 at 20:07

nneonneo

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