[Tutor] Help

Chris Kavanagh ckava1 at msn.com
Tue Nov 1 05:10:35 CET 2011

I'm going to thank Steven once again, and answer my own question in the 
2nd paragraph directly below (Steven hasn't had a chance to respond yet).

I just learned that the Function definitions are not read by the 
interpreter UNTIL they are called. I was reading them and assuming they 
were executed from the top down. Obviously I was getting somewhat 
confused because of this. This 'dragon' program makes much more sense to 
me now that I understand that. . .Thanks again Steven & everyone!!!
Happy Halloween!!!

On 10/31/2011 11:07 PM, Chris Kavanagh wrote:
> Yes Steven, that solved my question(s). It also cleared up what was to
> be my next question! Thanks so much. You might not realize how grateful
> I am to be able to have you & others on the list answer my questions.
> Just trust me when I say, I am grateful. And I apologize for the code
> being mangled on your end. I'm not sure why this happened, but you were
> correct in your assumptions. . .
> One thing I'm curious about. If the code is read by the Interpreter or
> Compiler from the top down, why in this case, does it not get confused
> (cause an error) when it hits line 30, if it doesn't yet know that
> {caveNumber=chooseCave()} and checkCave(caveNumber)}?? It seems to me in
> my limited experience, those last two lines should've come before line
> 30. It seems as though it would've made more sense to somehow put them
> before. In other languages, ala C++, don't global variables have to be
> declared at the 'top' of the code??
> On 10/31/2011 9:55 PM, Steven D'Aprano wrote:
>> Chris Kavanagh wrote:
>>> However, I'm confused on Line 30 {if chosenCave== str(friendlyCave)}.
>>> Here's the description of this line the author gives:
>>> "Here we check if the integer of the cave we chose ('1' or '2') is
>>> equal to the cave
>>> randomly selected to have the friendly dragon"
>>> My question is, we saved the integer of the cave we chose in the
>>> variable {cave}in line 15, not {chosenCave}. So, what the heck am I
>>> missing?? How is the {chosenCave} variable now holding the choice I
>>> made in the {cave} variable??
>> Unfortunately, the indentation of your code is completely mangled for
>> me, which makes it difficult to be sure which parts of the code are
>> inside functions and which are not. So I will be forced to guess.
>> I can tell that line 15 is inside the function chooseCave(), and so the
>> variable "cave" is a local variable. Local variables only exist inside
>> the function that creates them. In this case, the chooseCave() function
>> returns the value of "cave" to the caller.
>> That is, at the end of your code, you call the functions you earlier
>> created:
>> caveNumber = chooseCave()
>> checkCave(caveNumber)
>> These two lines cause the following to happen:
>> The function chooseCave() gets called. Execution shifts into the
>> function chooseCave:
>> 1 you are asked for a cave number
>> 2 your response is stored temporarily in the local variable "cave"
>> 3 and then returned to the caller
>> At this point, Python clears up the local variables, reclaiming their
>> memory ready for next time they are needed, and stores your response in
>> the global (top level) variable "caveNumber".
>> Next, you call the checkCave function with "caveNumber" as an argument.
>> This gets passed to the checkCave function, which sees it under the
>> local variable name "chosenCave". *Inside* the checkCave function, the
>> value which is known *outside* as "caveNumber" is known as "chosenCave".
>> And so inside the function, the line:
>> if chosenCave== str(friendlyCave)
>> works and the chosen cave number (known as "caveNumber" on the outside
>> and "chosenCave" on the inside) is compared to the friendly cave.
>> This might seem a bit confusing at first, but stick with it, it will
>> soon become completely natural.
>> Having different names for the same value in different contexts is a
>> good thing. It's a bit like how the same person might be called:
>> Mr President
>> Barrack Obama
>> Mr Obama
>> Barrack
>> Dad
>> Son
>> Bazza
>> depending on who is referring to him and under what circumstances. (That
>> last one might only be in Australia...)
>> The important thing to remember is this:
>> *Outside* of a function, all variables are *global*. You can't have two
>> global variables called "x" at the same time:
>> x = 1
>> x = 2
>> The second line replaces the value of x with a new value.
>> *Inside* a function, all variable assignments are *local*. (You can
>> change that with the "global" keyword, but you shouldn't.) A bit like
>> going to Los Angeles, what happens inside a function stays inside the
>> function. Local variable "x" doesn't interfere with global variable "x",
>> or with local "x" of any other function. The only way to get the value
>> of local "x" out and pass it to another function is with the return
>> statement.
>> I hope this helps.
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