import os, string
def replaceFile(oldname, newname):
""" Rename file 'oldname' to 'newname'.
"""
if os.name == 'nt' and os.path.exists(oldname):
# POSIX rename does an atomic replace, WIN32 rename does not. :-(
try:
os.remove(newname)
except OSError, exc:
import errno
if exc.errno != errno.ENOENT: raise exc
# rename it
os.rename(oldname, newname)
class FileMorpher:
""" A class that enables a client to securely update an existing file,
including the ability to make an automated backup version.
"""
def __init__(self, filename, **kw):
""" The constructor takes the filename and some options.
backup -- boolean indicating whether you want a backup file
(default is yes)
"""
self.filename = filename
self.do_backup = kw.get('backup', 1)
self.stream = None
self.basename, ext = os.path.splitext(self.filename)
def __del__(self):
if self.stream:
# Remove open temp file
self.__close()
os.remove(self.__tempfile())
def __tempfile(self):
return self.basename + ".tmp"
def __close(self):
""" Close temp stream, if open.
"""
if self.stream:
self.stream.close()
self.stream = None
def load(self):
""" Load the content of the original file into a string and
return it. All I/O exceptions are passed through.
"""
file = open(self.filename, "rt")
try:
content = file.read()
finally:
file.close()
return content
def save(self, content):
""" Save new content, using a temporary file.
"""
file = self.opentemp()
file.write(content)
self.commit()
def opentemp(self):
""" Open a temporary file for writing and return an open stream.
"""
assert not self.stream, "Write stream already open"
self.stream = open(self.__tempfile(), "wt")
return self.stream
def commit(self):
""" Close the open temp stream and replace the original file,
optionally making a backup copy.
"""
assert self.stream, "Write stream not open"
# close temp file
self.__close()
# do optional backup and rename temp file to the correct name
if self.do_backup:
replaceFile(self.filename, self.basename + ".bak")
replaceFile(self.__tempfile(), self.filename)
if __name__ == "__main__":
# prepare test file
test = open('foo.txt', 'wt')
test.write('\txxx\nline 2\n\t\t2 tabs\n')
test.close()
# load the file's content
file = FileMorpher('foo.txt')
text = file.load()
# detab it, this could also be done shorter by file.save()
stream = file.opentemp()
stream.write(string.expandtabs(text))
file.commit()
