[Python-Dev] linktree.py

[David MacQuigg]

Hello,

I'm new to Python, and I'm very impressed with the potential of this =
language to simplify much of the software my company provides.  As a =
first project, I'm looking to replace some tricky scripts written in csh =
for setting up our tool hierarchies.  An example is a script to =
construct a "mock hierarchy" out of some patch files and links to a =
production hierarchy.  Our hierarchies are typically two gigabytes, =
thousands of files, lots of strange links, many of which are broken.  So =
the script needs to be fairly robust.  The functions in 'shutil' won't =
do it.  'copytree' works, but the cost is a huge amount of disk space.  =
A mock hierarchy takes not much more space than the patch files =
themselves.

After a brief search on the Python website, I couldn't find a suitable =
utility, and decided to write my own (see below).  It seems like this =
could be a useful, general-purpose addition to 'shutil'.

I've tested this on a large hierarchy on a Solaris workstation, and it =
seems to work.  There are some dark corners which worry me however, so I =
thought I would get some advice from the experts.  Has anything like =
this already been done or is it planned?  Would a function like this be =
a useful addition to 'shutil'?  I'm intending to continue work on it, =
and will be glad to contribute it to the library.

import os, sys
from os.path import *

def linktree(oldtree, newtree):
  """linktree(oldtree, newtree) -> None
  Leave 'oldtree' undisturbed.  Recursively add links to 'newtree', =
until it
  looks just like 'oldtree', but with the new files patched in.=20
  """
  names =3D os.listdir(oldtree)
  print 'Candidates: ', names
  for name in names:
    oldpath =3D abspath(join(oldtree, name))
    newpath =3D abspath(join(newtree, name))
    if not exists(newpath) and not islink(newpath):
      if not exists(oldpath):  # Don't link to a bad link.
        print '*** Error ***\nPath does not exist:\n', oldpath
        continue
      print 'New link: ', newpath
      os.symlink(oldpath, newpath)  # OK if oldpath is a good link.
    elif isfile(newpath) and not islink(newpath):
      print 'As is: ', newpath=20
      pass  # Leave new files as is.
    elif isdir(newpath) and not islink(newpath):
      print 'Down one level \n', newpath
      linktree(oldpath, newpath)  # Recursive call
      print 'Up one level'
    else:
      print '*** Error ***\nNot a file or directory:\n', newpath

- Dave

*************************************************************     *
* David MacQuigg               * email:  macquigg@cadence.com  *  *
* Principal Product Engineer   * phone:  USA 520-721-4583      *  *  *
* Analog Artist                                                *  *  *
*                                * 9320 East Mikelyn Lane       * * *
* Cadence Design Systems, Inc.   * Tucson, Arizona 85710          *
*************************************************************     *=20