Question

Parsed the IANA subtag (see Cascaded string split, pythonic way) and made a list of 8600 tags:

tags= ['aa',
       'ab',
       'ae',
       'af',
       'ak',
       'am',
       'an',
       'ar',
       # ...

I want to check for example mytag="ro" if is in the list:
what is the fastest way to do that:

First solution:

if mytag in tags:
    print "found"

Second solution:

if mytag in Set(tags):
    print "found"

Third solution: Transform the list in a big string like: '|aa|ab|ae|af|ak|am|an|ar|...' and then see if string is in another string:

tags = '|aa|ab|ae|af|ak|am|an|ar|...'
if mytag in tags:
    print "found"

Is there another way? Which is the fastest, is this already measured, if not how can I benchmark myself (shoul I take a random element from the list or should I take the last and then test it, can someone provide python code for a ‘chronometer’)?

Answer 1

As I don’t have access to the original string, any test would be biased. However, you asked for a chronometer ? Check the timeit module, designed to time some code snippets.

Note that if you use IPython, %timeit is a magic function that makes it a breeze to time the execution of a function, as illustrated below.

Some comments

• you should replace Set by set…
• construct your set and long string before running any test
• Taking a random element from your tags list is the way to go indeed.

---

As an example of use of %timeit in IPython:

tags = ['aa','ab','ae','af','ak','an','ar']
tags_set = set(tags)
tags_str = "|".join(tags)

%timeit 'ro' in tags
1000000 loops, best of 3: 223 ns per loop
%timeit 'ro' in tags_set
1000000 loops, best of 3: 73.5 ns per loop
%timeit 'ro' in tags_str
1000000 loops, best of 3: 98.1 ns per loop