Lesson Objective
Learn how to store, create, edit and open files in Python.
mrahmedcomputing
KS3, GCSE, A-Level Computing Resources
Lesson 8. File Handling
Lesson Notes
Data Persistence
Many programs or scripts execute quickly and then terminate. However, unless we retain the output they produce, their efforts become futile.
To achieve 'data persistence', we aim to store the data generated by a program for future use.
This can be accomplished using various methods, including text files, binary files (such as images or sound), databases, and browser cookies. In our code, we read from and write/appended to these storage mechanisms.
Text Files
When developing data-collecting programs, it's essential to store the data for future use. One common approach is to create a text file and save it in the same directory as your Python file.
Text files are used to store a variety of data:
- books and business documents
- logs of events
- lists of names
- tables of data with various numbers of columns and rows
Four methods (modes)
"r" - Read - Default value. Opens a file for reading, error if the file does not exist.
"w" - Write - Opens a file for writing, creates the file if it does not exist.
"a" - Append - Opens a file for appending, creates the file if it does not exist.
"x" - Create - Creates the specified file, returns an error if the file exists.
Opening and Writing to a File
The “Open” command must be used to open files. The file is stored in a file object (f). File is opened in “Write” mode. It's good practice to close the file after use.
Code:
f = open("Txt_File.txt","w") f.write("Theres something in the file.\nCan we be friencs now?") f.close()
Cmd Output:
Reading from File
You can use read() to display all the content of the file line by line.
Code:
f = open("Txt_File.txt","r") print(f.read()) f.close()
Cmd Output:
Theres something in the file. Can we be friencs now?
readlines() displays all the content of a file as an array. This can be stored in a. Variable.
Code:
f = open("Txt_File.txt","r") print(f.readlines()) f.close()
Cmd Output:
['Theres something in the file.\n','Can we be friencs now?']
Modifying a Text File
Here is a text file:
Steps:
- File is opened in “Read” mode.
- The content of the file is stored as a list in the variable “shopping”.
- A section of the list is edited.
- File is opened in “Write” mode.
- The new file content is then written to the file using the “writelines” command.
Code:
f = open("Txt_File.txt","r") print(f.readlines()) f.close() print(shopping) shopping[3] = "Carrots\n" print("") f = open("Txt_File.txt","w") f.writelines(shopping) f.close() print(shopping)
Cmd Output:
['Apples\n', 'Banana\n', 'Pear\n', 'Egg\n', 'Milk\n', 'Bread\n', 'Orange\n', 'Pasta\n', 'Rice'] ['Apples\n', 'Banana\n', 'Pear\n', 'Carrots\n', 'Milk\n', 'Bread\n', 'Orange\n', 'Pasta\n', 'Rice']
Create a File
???
Code:
f = open("new_Txt_File.txt","x")
Cmd Output:
