Implementation
In this section, we will use the Command pattern to implement the most basic file utilities:
- Creating a file and optionally writing text (a string) to it
- Reading the contents of a file
- Renaming a file
- Deleting a file
We will not implement these utilities from scratch, since Python already offers good implementations of them in the os module. What we want is to add an extra abstraction level on top of them so that they can be treated as commands. By doing this, we get all the advantages offered by commands.
From the operations shown, renaming a file and creating a file support undo. Deleting a file and reading the contents of a file do no support undo. Undo can actually be implemented on delete file operations. One technique is to use a special trash/wastebasket directory that stores all the deleted files, so that they can be restored when the user requests it. This is the default behavior used on all modern desktop environments and is left as an exercise.
Each command has two parts...
