[Tutor] Generators

[Tiger12506]

> I am new to Python but not new to programming languages.  I have seen this
> "while 1" a lot.  In fact in other languages I would expect "while 1" to 
> be
> the same as "while TRUE".  I have used that in other languages, but in the
> definition below I would expect the "yield b..." to continue on until a
> "break".  So the question is, how does this work without going into an
> infinite loop without a break?
>
> Jeff

while 1:   and  while TRUE: mean the same thing.
The thing is - it is an infinite loop.

>>> a = fibonacci()
>>> a.next()
1
>>>

No matter how many times you call a.next(), it will continue to return 
numbers. You are being fooled by the yield statement. Generators are special 
objects.

The yield statement is ~~ difficult to translate into computer terms. My 
first impulse is to compare it to an interrupt, but you might not know what 
that is.

The best way to explain it is to litter that example with print statements.
Here:

def fibonacci():
  a = 1
  print "a = 1"

  b = 1
  print "b = 1"

  print "Before yield a"
  yield a
  print "After yield a"

  while 1:
    print "Before yield b"
    yield b
    print "After yield b"
    a, b = b, a+b
    print "After calculation"





>>> a = fibonacci()
>>> a.next()
a = 1
b = 1
Before yield a
1
>>> a.next()
After yield a
Before yield b
1
>>> a.next()
After yield b
After calculation
Before yield b
2
>>> a.next()
After yield b
After calculation
Before yield b
3
>>>


JS