Alex Bryan wrote:
Okay, so i don't really understand the Yield thing and i know it is
useful. I've read a few things about it but it is all programming jargon
and so basically it is hard for me to understand. So can anyone give me
a description or link me to a site that has a good definition and/or
examples of it? If you could I would really appreciate it.
Use yield when you want the function to act as a generator. That is each time
it is called it generates a response and returns it, but leaves its state intact
so that the next time you call it, it can pick up where it left off and continue on.
Best example I ever saw is the code that implements os.walk() function:
def walk(top, topdown=True, onerror=None):
"""
Example:
from os.path import join, getsize
for root, dirs, files in walk('python/Lib/email'):
print root, "consumes",
print sum([getsize(join(root, name)) for name in files]),
print "bytes in", len(files), "non-directory files"
if 'CVS' in dirs:
dirs.remove('CVS') # don't visit CVS directories
"""
from os.path import join, isdir, islink
try:
names = listdir(top)
except error, err:
if onerror is not None:
onerror(err)
return
dirs, nondirs = [], []
for name in names:
if isdir(join(top, name)):
dirs.append(name)
else:
nondirs.append(name)
if topdown:
yield top, dirs, nondirs
for name in dirs:
path = join(top, name)
if not islink(path):
for x in walk(path, topdown, onerror):
yield x
if not topdown:
yield top, dirs, nondirs
Actually this code uses yield and is recursive. Pretty neat.
-Larry
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