Re: Help me understand this iterator
- From: Peter Otten <__peter__@xxxxxx>
- Date: Tue, 31 Oct 2006 12:53:20 +0100
LaundroMat wrote:
Hi,
I've found this script over at effbot
(http://effbot.org/librarybook/os-path.htm), and I can't get my head
around its inner workings. Here's the script:
import os
class DirectoryWalker:
# a forward iterator that traverses a directory tree
def __init__(self, directory):
self.stack = [directory]
self.files = []
self.index = 0
def __getitem__(self, index):
while 1:
try:
file = self.files[self.index]
self.index = self.index + 1
except IndexError:
# pop next directory from stack
self.directory = self.stack.pop()
self.files = os.listdir(self.directory)
self.index = 0
else:
# got a filename
fullname = os.path.join(self.directory, file)
if os.path.isdir(fullname) and not
os.path.islink(fullname):
self.stack.append(fullname)
return fullname
for file in DirectoryWalker("."):
print file
Now, if I look at this script step by step, I don't understand:
- what is being iterated over (what is being called by "file in
DirectoryWalker()"?);
- where it gets the "index" value from;
- where the "while 1:"-loop is quitted.
With
dw = DirectoryWalker(".")
the for loop is equivalent to
index = 0 # internal variable, not visible from Python
while True:
try:
file = dw[index] # invokes dw.__getitem__(index)
except IndexError:
break
print file
This is an old way of iterating over a sequence which is only used when the
iterator-based approach
dwi = iter(dw) # invokes dw.__iter__()
while True:
try:
file = dwi.next()
except StopIteration:
break
print file
fails.
Peter
.
- References:
- Help me understand this iterator
- From: LaundroMat
- Help me understand this iterator
- Prev by Date: Re: How can I import a script with an arbitrary name ?
- Next by Date: Re: How can I import a script with an arbitrary name ?
- Previous by thread: Help me understand this iterator
- Next by thread: Re: Help me understand this iterator
- Index(es):
Relevant Pages
|
