bad generator performance

[Johannes Ahl mann]

hi,

i am in the process of profiling an application and noticed how much
time my depth first generator for walking a tree data structure took.

i wrote the same thing as a recursive function producing an array, and
this non-generator version is nearly 10 times faster!

any ideas why this is, what i did wrong...
for some reason the generator version appears as being called much more
often than the recursive one. no idea why that is, but the data is
definitely identical!

here the output from the python profiler and the respective code:

### snip ###

ncalls  tottime  percall  cumtime  percall filename:lineno(function)
94209/8191    0.560    0.000    0.590    0.000  :71(depthFirstIterator2)
4095/1    0.060    0.000    0.080    0.080  :62(depthFirstIterator1)

### snip ###
	
def depthFirstIterator1(self, depth = 0):
    ret = [[self, True, depth]]

    if self.isFolder():
      for c in self.children:
        ret = ret + c.depthFirstIterator(depth = depth + 1)

    return ret + [[self, False, depth]]

def depthFirstIterator2(self, depth = 0):
    yield [self, True, depth]

    if self.isFolder():
      for c in self.children:
        for y in c.depthFirstIterator(depth = depth + 1):
          yield y

    yield [self, False, depth]

### snip ###

i'd appreciate any comments or explanations why the generator might be
so much slower, as i had just decided to use generators more frequently
and in the respective PEP they are praised as generally fast.

thx,

Johannes