A demonstration of using a dict of callables instead of a chain of if/elif/elif branches

if_vs_dict

from timeit import timeit
import string

# If you have a chain of if and elif like this
# that you then use to decide a particular
# course of action
def ifelif(arg1, arg2):
    if arg1 == 'hello':
        return 'hi ' + arg2
    elif arg1 == 'namaskara':
        backwards_name = str(reversed(arg2))
        return 'susvagata ' + backwards_name
    elif arg1 == 'may the force be with you':
        return 'and also with you'

    raise ValueError('unknown greeting')


# You can instead create a dict, keyed on the greeting, with callables as the value.

def backwards_welcome(name):
    backwards_name = str(reversed(name))
    return 'susvagata ' + backwards_name


# The dict should be created outside of the function, either as a member of the object, class or module.
greetings = {
    'hello': lambda x: 'hi ' + x,
    # If it undesirable to use lambda (e.g. side-effects, too big, whatever)
    # define a function the old fashioned way.
    'namaskara': backwards_welcome,
    # The callables must all have the same number of arguments, even if you don't use them
    # or you can use *args,**kwargs to allow variable args.
    'may the force be with you': lambda _: 'and also with you',
}


# This makes the function look like this instead:
def by_dict(arg1, arg2):
    try:
        return greetings[arg1](arg2)
    except KeyError:
        raise ValueError('unknown greeting')


# At this scale, it doesn't make any difference to performance,
# So the choice is purely cosmetic, and subject to personal preference.
print('by ifs, first branch')
print(timeit(lambda: ifelif('hello', 'paul')))
print('by dict, first entry')
print(timeit(lambda: by_dict('hello', 'paul')))

print('by ifs, last branch')
print(timeit(lambda: ifelif('may the force be with you', 'paul')))
print('by dict, last entry')
print(timeit(lambda: by_dict('may the force be with you', 'paul')))

def bigif(arg):
  if(arg is None): return None
  elif(arg =="a"): return "hello"
  elif(arg =="b"): return "hello"
  elif(arg =="c"): return "hello"
  elif(arg =="d"): return "hello"
  elif(arg =="e"): return "hello"
  elif(arg =="f"): return "hello"
  elif(arg =="g"): return "hello"
  elif(arg =="h"): return "hello"
  elif(arg =="i"): return "hello"
  elif(arg =="j"): return "hello"
  elif(arg =="k"): return "hello"
  elif(arg =="l"): return "hello"
  elif(arg =="m"): return "hello"
  elif(arg =="n"): return "hello"
  elif(arg =="o"): return "hello"
  elif(arg =="p"): return "hello"
  elif(arg =="q"): return "hello"
  elif(arg =="r"): return "hello"
  elif(arg =="s"): return "hello"
  elif(arg =="t"): return "hello"
  elif(arg =="u"): return "hello"
  elif(arg =="v"): return "hello"
  elif(arg =="w"): return "hello"
  elif(arg =="x"): return "hello"
  elif(arg =="y"): return "hello"
  elif(arg =="z"): return "hello"
  elif(arg =="A"): return "hello"
  elif(arg =="B"): return "hello"
  elif(arg =="C"): return "hello"
  elif(arg =="D"): return "hello"
  elif(arg =="E"): return "hello"
  elif(arg =="F"): return "hello"
  elif(arg =="G"): return "hello"
  elif(arg =="H"): return "hello"
  elif(arg =="I"): return "hello"
  elif(arg =="J"): return "hello"
  elif(arg =="K"): return "hello"
  elif(arg =="L"): return "hello"
  elif(arg =="M"): return "hello"
  elif(arg =="N"): return "hello"
  elif(arg =="O"): return "hello"
  elif(arg =="P"): return "hello"
  elif(arg =="Q"): return "hello"
  elif(arg =="R"): return "hello"
  elif(arg =="S"): return "hello"
  elif(arg =="T"): return "hello"
  elif(arg =="U"): return "hello"
  elif(arg =="V"): return "hello"
  elif(arg =="W"): return "hello"
  elif(arg =="X"): return "hello"
  elif(arg =="Y"): return "hello"
  elif(arg =="Z"): return "hello"

bigdict = {k: lambda: 'hello' for k in string.ascii_letters}

# When you have a large set of choices, the dict wins hands down.
print('by ifs, first branch, big selection')
print(timeit(lambda: bigif('A')))
print('by dict, first entry, big_selection')
print(timeit(lambda: bigdict['A']()))
print('by ifs, last branch, big selection')
print(timeit(lambda: bigif('Z')))
print('by dict, last entry, big_selection')
print(timeit(lambda: bigdict['Z']()))