Working with Data Files
So far, the data we have used have all been either coded right into the program or have been entered by the user. In real life, data reside in files. For example, the images we worked within the image processing unit ultimately live in files on your hard drive. Web pages, and word processing documents, and music are other examples of data that live in files. In this topic we’ll introduce how to work with files to retrieve data from them.
For our purposes, we will assume that our data files are text files–that is, files filled with characters. The Python programs that you write are stored as text files. We can create these files in any of a number of ways. For example, we could use a text editor to type in and save the data. We could also download the data from a website and then save it in a file. Regardless of how the file is created, Python will allow us to manipulate the contents.
In Python, we must open files before we can use them, and close the files when we are done with them. As you might expect, once a file is opened it becomes a Python object just like all other data. The table below shows the functions and methods that can be used to open and close files.
| Method Name | Use | Explanation |
|---|---|---|
open | open(filename,'r') | Open a file called filename and use it for reading. This will return a reference to a file object. |
open | open(filename,'w') | Open a file called filename and use it for writing. This will also return a reference to a file object. |
close | fileRef.close() | File use is complete. |