Raw_input using python 2.7

Question

This is my function:

def mainMenu():
    print " Do you want to send a message(send) or add a name to the database(add) or exit the program(exit)?"
    answer = raw_input()
    print answer
    if answer is "send":
        sendMessage()
    elif answer is "add":
        addName()
    elif answer is "exit":
        sys.exit()
    else:
        print "Sorry, '%s' is not a valid input. Please use one 'send', 'add', or 'exit'" %answer

No matter what I enter the result in the else statement. The only thing I can really thing it is would be a problem with raw_input().

Here's a screenshot from the shell. The syntax highlighting is because I'm using sublimeREPL and it just does that, doesn't affect the code at all:

program output

I've tested all the functions that are called and they work fine individually

@MartijnPieters: Whoops. Not particularly "raw", then, is it? — Nemo
– Nemo, Commented May 10, 2015 at 1:49

Martijn Pieters · Accepted Answer · 2015-05-10 01:51:16Z

6

Try replacing is with ==.

For example:

In [1]: answer = raw_input()
arst

In [2]: answer
Out[2]: 'arst'

In [3]: answer == 'arst'
Out[3]: True

In [4]: answer is 'arst'
Out[4]: False

edited May 10, 2015 at 1:51

Martijn Pieters

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answered May 10, 2015 at 1:47

slcott

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4 Comments

Josh Gribbon Over a year ago

That worked! Thanks! I thought "is" was the same as "==" in python, but I guess there's some slight difference

slcott Over a year ago

"is" asks if two objects are the same object. "==" asks if two objects are equivalent. "is" really is just comparing the memory address and "==" just compares what is in that address. hope that clears it up.

Martijn Pieters Over a year ago

Whoops, that's what I get for not paying attention to the changing sort order! I edited your answer instead of mine, sowwy.

Josh Gribbon Over a year ago

So basically while two things may look the same they are stored separately in memory and are then not the same object. Very cool, thanks!

Martijn Pieters · Accepted Answer · 2015-05-10 01:52:33Z

3

You are using identity tests to compare strings. Users cannot possibly create the exact same string object when entering text; they create new string objects, with the same value contained, instead.

Don't use is, use == to test for equality; different objects with the same value:

if answer == "send":
    sendMessage()
elif answer == "add":
    addName()
elif answer == "exit":
    sys.exit()

See Understanding Python's "is" operator.

edited May 10, 2015 at 1:52

answered May 10, 2015 at 1:48

Martijn Pieters

1.1m326 gold badges4.2k silver badges3.4k bronze badges

3 Comments

Zulu Over a year ago

Related to your previous answer here: stackoverflow.com/questions/13650293/… ;)

Josh Gribbon Over a year ago

awesome, thanks for the explanation! Switching it worked but I was wondering why it wouldn't be the same, that makes sense.

Martijn Pieters Over a year ago

@Zulu: Thanks for saving me from searching! :-)

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