Listing 2. PathFinder.py
#!/usr/bin/env python
"""PathFinder.py
This module resolves pathnames relative to the
Python path."""
import sys, os
class Error(Exception): """Raised when a pathname
cannot be resolved."""
def find(pathname):
"""Resolve pathname to a location on the
Python path."""
if os.path.isabs(pathname):
return pathname
for dirname in sys.path:
candidate = os.path.join(dirname, pathname)
if os.path.isfile(candidate):
return candidate
raise Error("Cannot find %s on the Python path."
% `pathname`)
def main():
"""Module mainline (for standalone execution)"""
def testFind(path, expectError=0):
"""Try to resolve path, with diagnostic
messages."""
print "Resolving %s..." % path
try:
print find(path)
except Error, info:
if expectError:
print "As expected:", info
else:
print "ERROR:", info
# Try to find something known to be on the path,
using both
# relative and absolute paths.
testFind("socket.py")
join = os.path.join
socketPath = join(sys.prefix, join("lib",
join("python", "socket.py")))
testFind(socketPath)
# Try to find something which probably
doesn't exist.
testFind("I_Dont_Exist.nonexistent_path", 1)
if __name__ == "__main__":
main()
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