Python return values?

Question

How do I do this? Can I do this?

def aFunction(argument):  
    def testSomething():  
        if thisValue == 'whatItShouldBe':  
            return True  
        else:  
            return False  

    if argument == 'theRightValue': # this is actually a switch using elif's in my code  
        testSomething()  
    else:  
        return False  

def aModuleEntryPoint():  
    if aFunction(theRightValue) == True:  
        doMoreStuff()  
    else:  
        complain()  

aModuleEntryPoint()

aModuleEntryPoint() needs to first make sure that a condition is true before it starts doing things. Because of encapsulation, aModuleEntryPoint doesn't know how to check the condition, but aFunction() has a sub-function called testSomething() that does know how to check the condition. aModuleEntryPoint() calls aFunction(theRightValue).

Because theRightValue was passed to aFunction() as an argument, aFunction() calls testSomething(). testSomething() performs the logic test, and either returns True or False.

I need for aModuleEntryPoint() to know what testSomething() decided. I do not want aModuleEntryPoint() to know anything about how testSomething() came to its conclusion.

It would actually be an accomplishment to post my actual source while removing other functions and what-not, so I had to setup the general gist like this.

thanks @Eimantas, this makes my head hurt less now :)

jcomeau_ictx
– jcomeau_ictx

2011-04-10 06:07:49 +00:00
Commented Apr 10, 2011 at 6:07 — jcomeau_ictx
– jcomeau_ictx, Commented Apr 10, 2011 at 6:07

the Tin Man · Accepted Answer · 2014-04-07 23:24:36Z

4

The only thing I see wrong right now is you need a return before testSomething() on line 9.

edited Apr 7, 2014 at 23:24

the Tin Man

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answered Apr 10, 2011 at 6:10

jcomeau_ictx

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2 Comments

jcomeau_ictx Over a year ago

short attention span. i tried to edit, then forgot the name of the function :^\

brad Over a year ago

perfect! I added return testSomething() in the switch, and works as expected. :-)

Eli Bendersky · Accepted Answer · 2011-04-10 06:19:50Z

0

Perhaps a sub-function is not the right encapsulation tool for you here. You want to expose internal functionality to an external entity. Python classes provide a better mechanism for expressing this than sub-function. Having a class, you can expose whatever parts of internal functionality you want in a very controlled manner.

answered Apr 10, 2011 at 6:19

Eli Bendersky

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1 Comment

brad Over a year ago

thank you! I will give that a whirl a little down the road when I'm not on such a time constraint.

David Z · Accepted Answer · 2011-04-10 06:25:03Z

0

My first thought upon looking at your code is that it's a little too complicated. Why have aFunction at all? You could just write

def aModuleEntryPoint():
    argument = ...
    if argument in (theRightValue, theOtherRightValue, theOtherOtherRightValue)\
       and testSomething():
        doMoreStuff()
    else:
        complain()

This if clause will first check whether argument is one of the possible right values, and if it is, then it will proceed to call testSomething() and check the return value of that. Only if that return value is true will it call doMoreStuff(). If either of the tests fails (that's why I used and), it will complain().

answered Apr 10, 2011 at 6:25

David Z

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2 Comments

brad Over a year ago

like I mentioned in the post, because of data encapsulation, aFunction() knows how to do things that others dont. In real life, aFunction() is called control(). It's purpose is to control the connection to sql. testSomething() is called checkConnection(), and verifies a good link to the database before the user of the program goes through the hassle of inputting data, only to be told the link failed.

David Z Over a year ago

@brad: ok, well it wasn't really clear from your question that aFunction contained enough code to justify making it its own function.

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