"Pythonic" equivalent for handling switch and multiple string compares

Question

Alright, so my title sucked. An example works better:

input = 'check yahoo.com'

I want to parse input, using the first word as the "command", and the rest of the string as a parameter. Here's the simple version of how my non-Pythonic mind is coding it:

if len(input) > 0:
    a = input.split(' ')
    if a[0] == 'check':
        if len(a) > 1:
            do_check(a[1])
    elif a[0] == 'search':
        if len(a) > 1:
            do_search(a[1])

I like Python because it makes normally complicated things into rather simple things. I'm not too experienced with it, and I am fairly sure there's a much better way to do these things... some way more pythonic. I've seen some examples of people replacing switch statements with dicts and lambda functions, while other people simply recommended if..else nests.

Answer 1

dispatch = {
  'check': do_check,
  'search': do_search,
}
cmd, _, arg = input.partition(' ')
if cmd in dispatch:
    dispatch[cmd](arg)
else:
    do_default(cmd, arg)

Answer 2

If you're looking for a one liner 'pythonic' approach to this you can use this:

def do_check(x): print 'checking for:', x
def do_search(x): print 'searching for:', x

input = 'check yahoo.com'
{'check': do_check}.get(input.split()[0], do_search)(input.split()[1])
# checking for: yahoo.com

input = 'search google.com'
{'check': do_check}.get(input.split()[0], do_search)(input.split()[1])
# searching for: google.com

input = 'foo bar.com'
{'check': do_check}.get(input.split()[0], do_search)(input.split()[1])
# searching for: bar.com

Answer 3

This lets you avoid giving each command name twice; function names are used almost directly as command names.

class CommandFunctions:
    def c_check(self, arg):
        print "checking", arg

    def c_search(self, arg):
        print "searching for", arg

    def c_compare(self, arg1, arg2):
        print "comparing", arg1, "with", arg2

    def execute(self, line):
        words = line.split(' ')
        fn = getattr(self, 'c_' + words[0], None)
        if fn is None:
            import sys
            sys.stderr.write('error: no such command "%s"\n' % words[0])
            return
        fn(*words[1:])

cf = CommandFunctions()
import sys
for line in sys.stdin:
    cf.execute(line.strip())

Answer 4

I am fairly sure there's a much better way to do these things... some way more pythonic.

Not really. You code is simple, clear, obvious and English-like.

I've seen some examples of people replacing switch statements with dicts and lambda functions,

Yes, you've seen them and they're not clear, obvious or English-like. They exist because some people like to wring their hands over the switch statement.

while other people simply recommended if..else nests.

Correct. They work. They're simple, clear, ...

Your code is good. Leave it alone. Move on.

Answer 5

Disregard, I just realized that my answer was similar to one of the other answers - and apparently there's no delete key :)

Answer 6

Variation on @MizardX's answer:

from collections import defaultdict

dispatch = defaultdict(do_default, check=do_check, search=do_search)
cmd, _, arg = input.partition(' ')
dispatch[cmd](arg)