pombredanne / inplace

In-place file processing in Python

The inplace module provides Python classes for reading & writing a file "in-place": data that you write ends up at the same filepath that you read from, and inplace takes care of all the necessary mucking about with temporary files for you.

For example, given the file somefile.txt:

'Twas brillig, and the slithy toves
    Did gyre and gimble in the wabe;
All mimsy were the borogoves,
    And the mome raths outgrabe.

and the program disemvowel.py:

import inplace

with inplace.InPlace('somefile.txt') as fp:
    for line in fp:
        fp.write(''.join(c for c in line if c not in 'AEIOUaeiou'))

after running the program, somefile.txt will have been edited in place, reducing it to just:

'Tws brllg, nd th slthy tvs
    Dd gyr nd gmbl n th wb;
ll mmsy wr th brgvs,
    nd th mm rths tgrb.

and no sign of those pesky vowels remains! If you want a sign of those pesky vowels to remain, you can instead save the file's original contents in, say, somefile.txt~ by constructing the filehandle with:

inplace.InPlace('somefile.txt', backup_ext='~')

or save to someotherfile.txt with:

inplace.InPlace('somefile.txt', backup='someotherfile.txt')

Compared to the in-place filtering implemented by the Python standard library's fileinput module, inplace offers the following benefits:

• Instead of hijacking sys.stdout, a new filehandle is returned for writing.
• The filehandle supports all of the standard I/O methods, not just readline().
• There are options for setting the encoding, encoding error handling, and newline policy for opening the file, along with support for opening files in binary mode, and these options apply to both input and output.
• The complete filename of the backup file can be specified; you aren't constrained to just adding an extension.
• When used as a context manager, inplace will restore the original file if an exception occurs.
• The creation of temporary files won't silently clobber innocent bystander files.