Repeat python function and return value

Question

I am trying to have a function repeat itself if a certain criteria is not met. For instance:

def test():
    print "Hello",
    x = raw_input()
    if x in '0123456789':
        return x
    test()

In this program if you type a number the first time, it will return the number. If you type some non-number, it will repeat itself as desired. However, if you type some non-numbers and then a number, it will return nothing. Why is that the case?

It should work if you replace test() with return test(). — Holger
– Holger, Commented Oct 11, 2012 at 22:43
If you want to repeat a prompt until you get valid input I'd suggest using a while loop rather than recursion. Every time the input is invalid you get another frame pushed on the stack. Probably not a big deal for what you're doing, but no harm in being tidy. — cjm
– cjm, Commented Oct 11, 2012 at 22:47
@cjm, if what you're doing is "learning to program" it is a big deal. But mistakes can be a good thing if you learn from them. — John La Rooy
– John La Rooy, Commented Oct 11, 2012 at 23:28

Mike Corcoran · Accepted Answer · 2012-10-11 22:43:56Z

8

you need to return test() at the tail of the function to return the value that the valid call into test() returns.

answered Oct 11, 2012 at 22:43

Mike Corcoran

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Comments

John La Rooy · Accepted Answer · 2012-10-11 23:10:14Z

4

The way you are having test call itself is the wrong way to do it. Each time your program restarts the function, you will use up another level of stack. Eventually the program will stop(crash) even if the user never inputs one of those characters.

def test():
    while True:
        print "Hello",
        x = raw_input()
        if x in '0123456789':
            return x

answered Oct 11, 2012 at 23:10

John La Rooy

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1 Comment

jsbueno Over a year ago

You know you are right, and you know the code you posted is simply not fun. :-) But, the code will work the way the o.p. envisioned - for this purpose - @mikecorcoran's answer has the real problem nailed.

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