File Handling
Coding: Introduction to Python v3, topic 2.2.1
Files
Without files we can only store data in the memory.
Files
- Files allow us to store data so that it persists even when our program is not running.
- This allows programs to 'carry on where they left off' when they are executed.
Text files
- Text files consist of string data that can be read and processed by many applications.
Binary files
- Binary files consist of binary data that is read and processed by specific applications.
File Handling
We must be careful with the way that we access files so that we do not accidentally corrupt them.
Open the file
- First, we open the file for use, so that the program can read from or write to it.
- We can do this using:
- open("filename.txt", "r")
- open("filename.txt", "w")
- Opening with "r" will allow you to read from the file.
- Opening with "w" will allow you to write to the file
Assign the file to a variable
- The file must be assigned to a variable so that we can keep referring to it.
- This can be done as follows:
- myFile = open("filename.txt", "r")
- myFile = open("filename.txt", "w")
Read / write
- We can now read or write to the file using the following commands:
- myFile.readline() will return the next line of a file as a string.
- myFile.write(
) will write a line to the file.
Close the file
- Finally, we must close the file so that it is free for another program to access.
- We can do this using:
- myFile.close()
Test yourself on File Handling
What does a text file contain?
What is the main reason to use files?
File Handling
Which of these are valid file handling methods?
If we don't use the correct methods to access files, what might happen?