Newbie definining functions question

[Marv73]

Ok, I'm going through the documentation (the informal introduction to 2.0 part) and I'm a little confused about defining functions. It gives this example of the Fibonacci sequence:

>>> def fib: # write Fibonacci series up to n
... "Print a Fibonacci series up to n"
... a, b = 0, 1
... while b < n:
... print b,
... a, b = b, a+b
...
>>> # Now call the function we just defined:
... fib(2000)
1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597

Now keep in mind, I'm moving to python from C++

Ok, first of all the Fibonacci function is recursive right? Well I don't see any calls to fib within the function, what's with that? =P

Next, what does &quot;a, b = 0, 1&quot; do? To me it would seem it declares a, assigns b to 0, and then prints one or declares it or something =P

And why is it when I try, &quot;a = 0, b = 0, 1&quot; it says it can't assign to literal? I just typed that in trying t figure out what the a, b = 0, 1 did. [sig][/sig]

 

[2ffat]

First, This function is not recursive. All the work is being done in a while loop. The key is &quot;while b < n&quot;.

Second, the variable a is being assigned to 0 and b is assigned to 1 in &quot;a, b = 0, 1&quot;. The same thing is happening in the while loop, &quot;a, b = b, a+b.&quot; In this case, the value of b is assigned to a, then b gets the &quot;old&quot; value of a plus the value of b.

Lets trace this a little and see what is happening. We'll start with the while loop:
while b < n: [tab]a = 0, b = 1, n = 2000, so this is true since 1 < 2000
[tab]print b, [tab]1 is printed
[tab]a, b = b, a+b [tab]a = 1, b = 0+1 (zero is the old value of a)

Second time through:
while b < n: [tab]a = 1, b = 1, n = 2000, so this is true since 1 < 2000
[tab]print b, [tab]1 is printed
[tab]a, b = b, a+b [tab]a = 1, b = 1+1 (1 is the old value of a)

Third time through:
while b < n: [tab]a = 1, b = 2, n = 2000, so this is true since 2 < 2000
[tab]print b, [tab]2 is printed
[tab]a, b = b, a+b [tab]a = 2, b = 2+1

Fourth time through:
while b < n: [tab]a = 2, b = 3, n = 2000, so this is true since 3 < 2000
[tab]print b, [tab]3 is printed
[tab]a, b = b, a+b [tab]a = 3, b = 3+2

And so on. A C++ program might look like:

void feb(int n)
{
[tab]int a = 0;
[tab]int b = 1;

[tab]while (b < n)
[tab]{
[tab][tab]cout << b << &quot; &quot; << flush;
[tab][tab]int holda = a;
[tab][tab]a = b;
[tab][tab]b += holda;
[tab]}
}

Or something like it. Hope this helps.





[sig]<p>James P. Cottingham<br><a href=mailto: > </a><br><a href=

http://www.ivcusa.com>International

Veneer Co., Inc.</a><br>All opinions are mine alone and do not necessarily reflect those of my employer.[/sig]

 

[Marv73]

Ok, I see the mistake I made.

I didn't realize that you put all the variables you wanted to sign, and then each of there assignments. You certainly don't do a,b = 1,2 in C++

Thanks for clearing that up [sig][/sig]