Corpus readers and views are all read-only, but there will be times when you want to add to or edit the corpus files. However, modifying a corpus file while other processes are using it, such as through a corpus reader, can lead to dangerous undefined behavior. This is where file locking comes in handy.
You must install the lockfile library using sudo easy_install lockfile or sudo pip install lockfile. This library provides cross-platform file locking, and so will work on Windows, Unix/Linux, Mac OS X, and more. You can find detailed documentation on lockfile at http://packages.python.org/lockfile/.
Here are two file editing functions: append_line() and remove_line(). Both try to acquire an exclusive lock on the file before updating it. An exclusive lock means that these functions will wait until no other process is reading from or writing to the file. Once the lock is acquired, any other process that tries to access the file will...
