Alternative to eval in Python

Question

Python eval is quite slow. I need to evaluate simple boolean expression with logical operators (like "True or False"). I am doing this for thousands of line of data and eval is a huge bottleneck in terms of performance. It's really slow.. Any alternative approaches?

I tried creating a dict of possible expression combinations and their expected output, but this is really ugly!

I have the following code at the moment:

eval('%s %s %s' % (True, operator, False))

What exactly are you doing? In 99% of the cases people who use eval really don't need it and will be much better of without it. I'm pretty sure you're in this group. — George Karpenkov
– George Karpenkov, Commented Oct 24, 2011 at 23:11
well, i just need to evaluate the boolean expression for thousands of lines. as you said, i do fall in the 99% category. the solution below is amazing! — user955632
– user955632, Commented Oct 24, 2011 at 23:18

Cat Plus Plus · Accepted Answer · 2011-10-24 23:11:31Z

14

import operator ops = { 'or': operator.or_, 'and': operator.and_ } print ops[op](True, False)

answered Oct 24, 2011 at 23:11

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Comments

PaulMcG · Accepted Answer · 2011-10-25 01:09:21Z

It's not clear to me how @CatPlusPlus's solution will evaluate any boolean expression. Here is an example from the pyparsing wiki examples page of a Boolean expression parser/evaluator. Here are the test cases for this script:

p = True q = False r = True test = ["p and not q", "not not p", "not(p and q)", "q or not p and r", "q or not (p and r)", "p or q or r", "p or q or r and False", ] for t in test: res = boolExpr.parseString(t)[0] print t,'\n', res, '=', bool(res),'\n'

I have implemented a parser that converts the complex expression into simple boolean expressions (precedence of operators, brackets etc.). At the end of the day I only need to evaluate something like "True or False" etc. so that's why the above solution works for me!

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