Walk thru each subdirectory from a top directory

[silverburgh.meryl at gmail.com]

i am trying to use python to walk thru each subdirectory from a top
directory.  Here is my script:

savedPagesDirectory = "/home/meryl/saved_pages/data"

dir=open(savedPagesDirectory, 'r')

for file in dir:
    if (isdir(file)):
        # get the full path of the file
        fileName = savedPagesDirectory + file + 'index.html'
        print fileName

$ ./scripts/regressionTest.py
Traceback (most recent call last):
  File "./scripts/regressionTest.py", line 12, in ?
    dir=open(savedPagesDirectory, 'r')
IOError: [Errno 21] Is a directory

But I get the above error:

Can you please tell me what did I do wrong?

Thank you.