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Part 1: Programming & Python BasicsPart 2: Data Structures & FunctionsPart 3: Advanced Python & AI Foundation

Module 14: File Handling

In this module, we will learn about File Handling. This allows us to store data permanently in text files (.txt) on the hard disk, so the data remains saved even after the program stops running.

14.1 What is a File?​

Variables and lists store data in RAM. This data is temporary and disappears when the program stops. Files store data permanently on your disk.

We use the built-in open() function to work with files.

Common File Modes:​

  • 'r' (Read): Opens a file for reading (throws an error if the file does not exist).
  • 'w' (Write): Opens a file for writing (creates a new file if missing, or overwrites existing content).
  • 'a' (Append): Opens a file for adding data at the end (does not delete existing data).

14.2 Reading Files​

Here is how to open and read a file's content:

# open(file_path, mode)
file = open("sample.txt", "r")
content = file.read()
print(content)
file.close() # Always close the file to free up system resources

Using the with keyword is safer because Python automatically closes the file for you, even if an error happens.

with open("sample.txt", "r") as file:
    content = file.read()
    print(content)

14.3 Writing Files​

To write data into a file, open it in 'w' mode:

with open("output.txt", "w") as file:
    file.write("Hello, this file is created by Python!\n")
    file.write("Writing code is awesome.")

Note: If output.txt already exists, this command clears all its old content and replaces it with the new text.

14.4 Appending Files​

To add new lines to the end of a file without deleting the old content, use the 'a' (append) mode:

with open("output.txt", "a") as file:
    file.write("\nAdding this new line at the end using Append mode.")

14.5 Reading a File Line-by-Line​

For large files, it is better to read them line-by-line using a for loop to save memory:

with open("lines.txt", "r") as file:
    for line in file:
        print(line.strip()) # strip() removes extra blank lines/spaces

:::tip Real-World Use Case File handling is essential for reading server log files, importing CSV reports, or saving simple user preferences! :::

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