breaking iteration of generator method

[Brian]

Hello;

What happens when a program breaks (think keyword 'break') its iteration
of a generator? Is the old state in the generator preserved?

Ex:

# .gen() is generator method.

for i in myObject.gen():
if i == specialValue:
break

Do subsequent calls to .gen() start off with new locals? Or, would
the iteration begin after the yielded 'i' that caused the for-statement
to exit?


Many thanks,

Brian.

 

[Hans Nowak]

Hello;

What happens when a program breaks (think keyword 'break') its iteration
of a generator? Is the old state in the generator preserved?

Ex:

# .gen() is generator method.

for i in myObject.gen():
if i == specialValue:
break

Do subsequent calls to .gen() start off with new locals? Or, would
the iteration begin after the yielded 'i' that caused the for-statement
to exit?

It's easy to find out...
.... for i in range(10):
.... yield i
....
.... if x == 4:
.... break
.... else:
.... print x,
....
0 1 2 3.... print x,
....
5 6 7 8 9
However, if you use g() rather than an existing generator object, a new
generator will be created:
.... if x == 4:
.... break
.... else:
.... print x,
....
0 1 2 3.... print x,
....
0 1 2 3 4 5 6 7 8 9
HTH,

 

[Tim Hochberg]

Hello;

What happens when a program breaks (think keyword 'break') its iteration
of a generator? Is the old state in the generator preserved?

Ex:

# .gen() is generator method.

for i in myObject.gen():
if i == specialValue:
break

Do subsequent calls to .gen() start off with new locals?

It depends on how you do it. This::


for i in myObject.gen():
if i == specialValue:
break
# ...
for i in myObject.gen():
if i == otherSpecialValue:
break
# ...

Will start start with a new generator with new local each time since
each call to gen() creates a fresh generator. If you want to preserve
generator state between loop, what you do is::

generator = myObject.gen()
for i in generator:
if i == specialValue:
break
# ...
for i in generator:
if i == otherSpecialValue:
break
# ...

In this case, the same generator is used in each loop and the state is
preserved.

-tim

 

[Peter Otten]

Hello;

What happens when a program breaks (think keyword 'break') its iteration
of a generator? Is the old state in the generator preserved?

Ex:

# .gen() is generator method.

for i in myObject.gen():
if i == specialValue:
break

Do subsequent calls to .gen() start off with new locals? Or, would
the iteration begin after the yielded 'i' that caused the for-statement
to exit?


Many thanks,

Brian.

Running the following little demo should answer you questions.
The Mark class is used only to show when the generator dies, it relies on
CPython's garbage collection algorithm.

class Mark(object):
def __init__(self):
print "created"
def __del__(self):
print "gone"

def gen():
mark = Mark()
for i in range(10):
yield i


for i in gen():
print i,
if i == 5:
print "breaking"
break

g = gen()
for i in g:
print i,
if i == 5:
print "breaking"
break

while True:
print g.next()

Peter