yield

Robert Brewer fumanchu at amor.org
Sat Jan 17 21:01:48 CET 2004


Gerrit Holl wrote:
Gerrit Holl wrote:
> If a generator reaches a 'yield' statement, it returns
> the result of the expression behind the 'yield' statement.
> ...When you call the 'next' method of the generator, the
> body is executed, until it reaches a 'yield' statement.
> When you call the body again, it is executed again, until
> it reaches a 'yield' statement again,

A bit more explicitly (so as not to mislead the original poster):

When you call the body again, the function "picks up where it left off"
rather than "it is executed again". Example:

>>> def gen():
... 	x = 0
... 	while x < 5:
... 		yield x
... 		x += 1
... 		
>>> [a for a in gen()]
[0, 1, 2, 3, 4]

If it were "executed again", you'd be rebinding x to 0 each time, and
would never exit the while loop, nor would x be incremented. However,
since it "picks up where it left off" (i.e. the yield statement), x is
incremented and the while loop continues until x == 5.


Robert Brewer
MIS
Amor Ministries
fumanchu at amor.org




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