"choose" in Python?
 

There's a function that repeatedly shows up in languages, usually with more or less the following form (Python syntax):

var1 = raw_input("Input a number between one and three.")



choose var1:

   case "1":

      print "You inputted one."

   case "2":

      print "You inputted two."

   case "3":

      print "You inputted three."

Or something like that. I've also seen it called "switch." Does Python have anything like this?

Re: "choose" in Python?
 

In Python you can set up a dictionary to mimic switch/case ...

def choose(s):

    return {

    '1' : lambda:"You inputted one.",

    '2' : lambda:"You inputted two.",

    '3' : lambda:"You inputted three."

    }[s]()



var1 = raw_input("Input a number between one and three.")

print choose(var1)

Even in C the switch/case statement is not as efficient as multiple if/elif statements, so Python did not implement it.

Re: "choose" in Python?
 

That is pretty ingenious!
Does it work without using lambda? e.g
'1':"w/e", etc

Re: "choose" in Python?
 

Actually, in this case you don't need lambda, since you are only returning a string. Please shorten the code to ...

def choose(s):

    return {

    '1' : "You inputted one.",

    '2' : "You inputted two.",

    '3' : "You inputted three."

    }[s]



var1 = raw_input("Input a number between one and three.")

print choose(var1)

Mildy more elegant ...

def choose(s):

    return "You entered " + {

    '1' : "one",

    '2' : "two",

    '3' : "three"

    }[s]



var1 = raw_input("Input a number between one and three: ")

print choose(var1)

Re: "choose" in Python?
 

And, um, while we're at it...what does Lambda do, anyway?

Re: "choose" in Python?
 

Lambda creates an anonymous function, and is used to create a short inline function.

Lambda calculus is part of functional programming. It simply states that all computational constructs can be defined in terms of lambda. Interested? Read the article in:
http://linuxgazette.net/109/pramode.html

Re: "choose" in Python?
 

I'm going to feel really stupid when I see the answer to my question, because I'm sure I've seen it before and I've just forgotten. Anyway, I was just fiddling with this example, and I can't remember how to add a default case. In the example given I want to return the text "Bad input" for any value other than 1, 2, or 3. What do I need to add to the dictionary?

Re: "choose" in Python?
 

The standard try/except way would be:

def choose(s):

    try:

        return "You entered " + {

        '1' : "one",

        '2' : "two",

        '3' : "three"

        }[s]

    except:

        return "Bad input"



var1 = raw_input("Input a number between one and three: ")

print choose(var1)

Or straight foreward with dictionary method get():

def choose2(s):

    return "You entered " + {

    '1' : "one",

    '2' : "two",

    '3' : "three"

    }.get(s, "a bad number")



var1 = raw_input("Input a number between one and three: ")

print choose2(var1)

This is closer to the switch/case default.

Re: "choose" in Python?
 

Thanks, I knew it was something simple that I had seen before.

* SLAPS FOREHEAD *