Using if/elif/else for a "switch" in python

Question

While using the following code:

url = None
print("For 'The Survey of Cornwall,' press 1")
print("For 'The Adventures of Sherlock Holmes,' press 2")
print("For 'Pride and Prejudice,' press 3")
n = input("Which do you choose?")
if n==1:
    url = 'http://www.gutenberg.org/cache/epub/9878/pg9878.txt' #cornwall
    print("cornwall")
elif n==2:
    url = 'http://www.gutenberg.org/cache/epub/1661/pg1661.txt' #holmes
    print("holmes)
elif n==3:
    url = 'http://www.gutenberg.org/cache/epub/1342/pg1342.txt' #pap
    print("PaP")
else:
    print("That was not one of the choices")

I'm only getting the "else" case returned, why might that be??

also, there's a quote missing after "holmes. Just letting you know. — sk29910
– sk29910, Commented May 12, 2013 at 4:28

Ashwini Chaudhary · Accepted Answer · 2013-05-12 04:27:15Z

4

input() returns a string in py3x. So, you need to convert it to int first.

n = int(input("Which do you choose?"))

Demo:

>>> '1' == 1
False
>>> int('1') == 1
True

answered May 12, 2013 at 4:27

Ashwini Chaudhary

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5 Comments

Deivore Over a year ago

cool, thanks guys, gonna pick this one as the answer when the timer expires!

sapi Over a year ago

Also, if you just want a string (which you can then convert to an int), you should be using raw_input. input is unsafe, as it runs eval on what the user types.

Ashwini Chaudhary Over a year ago

@sapi OP is usong py3x not py2x, and raw_input has been renamed to input in py3x.

sapi Over a year ago

@AshwiniChaudhary - my mistake. I didn't notice that from the OP.

PaulMcG Over a year ago

@sapi - actually, I don't think the OP ever actually said, but if he/she were running Py2, then the code would have run okay as-is, as the Py2 behavior of input was to also do an implicit eval on the string before returning it.

Mike Pelley · Accepted Answer · 2013-05-12 04:27:12Z

3

input() returns a string, but you are comparing it to integers. You can convert the result from input to an integer with the int() function.

answered May 12, 2013 at 4:27

Mike Pelley

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Comments

Bear · Accepted Answer · 2013-05-12 04:27:05Z

1

You should convert the input with int() n = input("Which do you choose?") should be n = int(input("Which do you choose?")) This is due to the fact that input returns strings for all input since it should almost always work.

answered May 12, 2013 at 4:27

Bear

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Comments

PaulMcG · Accepted Answer · 2013-05-12 04:28:33Z

1

I'm guessing you are using Python 3, in which input behaves like raw_input did in Python 2, that is, it returns the input value as a string. In Python, '1' does not equal 1. You'll have to convert the input string to an int using n = int(n), then go through your succession of elifs.

answered May 12, 2013 at 4:28

PaulMcG

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Comments

TeknasVaruas · Accepted Answer · 2013-05-12 04:57:50Z

1

input() returns a string type. So, you need to convert your input into an integer using int(), or else you can compare the inputs to characters instead of integers, like '1', '2'.

answered May 12, 2013 at 4:57

TeknasVaruas

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Comments

Blckknght · Accepted Answer · 2013-05-12 05:24:52Z

While the other answers correctly identify the reason you're getting the else block in your current code, I want to suggest an alternative implementation that is a bit more "Pythonic". Rather than a bunch of nested if/elif statements, use a dictionary lookup, which can support arbitrary keys (including perhaps more meaningful ones than integers):

book_urls = {'cornwall': 'http://www.gutenberg.org/cache/epub/9878/pg9878.txt',
             'holmes': 'http://www.gutenberg.org/cache/epub/1661/pg1661.txt',
             'p and p': 'http://www.gutenberg.org/cache/epub/1342/pg1342.txt'}

print("For 'The Survey of Cornwall,' type 'cornwall'")
print("For 'The Adventures of Sherlock Holmes,' type 'holmes'")
print("For 'Pride and Prejudice,' type 'p and p'")

choice = input("Which do you choose?") # no conversion, we want a string!

try:
    url = book_urls[choice]
except KeyError:
    print("That was not one of the choices")
    url = None

You could make the whole thing data-driven if you wanted, with the book names and urls being provided as an argument to a function that would ask the user to pick one (without knowing what they were ahead of time).

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