Class 12 Computer Science Python Text Files

Python File Handling: Your Gateway to Persistent Data

What is File Handling?

Imagine you’re working on a Python program that collects user information or processes data. What happens when you close the program? File handling is how we make data persistent – saving it to stay even after our program stops running!

Think of it like saving your game progress or writing notes in a notebook that you can reopen later. File handling allows your Python programs to:

Remember data between sessions

Share information with other programs

Process large datasets efficiently

Create configuration files and reports

Why Learn File Handling?

Real-World Applications:

✅ Save user preferences and game scores

✅ Process log files and data exports

✅ Create and read configuration files

✅ Build data analysis pipelines

✅ Generate reports and documents

What is difference between text, binary and csv file

Here’s a clear breakdown of the differences between text, binary, and CSV files:

📄 Text Files
Format: Human-readable characters (ASCII or Unicode).

Usage: Stores plain text like documents, code, or logs.

Extensions: .txt, .html, .py, etc.

Editing: Can be opened and edited with any text editor.

Structure: Data is stored line by line, often separated by newline characters.

💾 Binary Files
Format: Machine-readable, stored as a stream of bytes.

Usage: Stores complex data like images, audio, executables.

Extensions: .exe, .jpg, .mp3, .dat, etc.

Editing: Requires specific software or programs to interpret.

Structure: No standard delimiters; data is encoded in binary format.

📊 CSV (Comma-Separated Values) Files
Format: Text-based but structured in tabular form.

Usage: Stores spreadsheet-like data; widely used for data exchange.

Extensions: .csv

Editing: Can be opened with text editors or spreadsheet software like Excel.

Structure: Each line represents a row; values are separated by commas.

🔍 Summary Table

file = open("example.txt", "r")

file = open("filename.txt", "mode")

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

with open("example.txt", "w") as file:
    file.write("Hello, world!")

Functions to read data from text file in Python

In Python, there are several functions to read data from a text file, each suited for different use cases. Here are the three main functions used to read data from text files, along with two examples for each:

📘 1.  read( ) 

Reads the entire content of the file as a single string.

✅ Example 1: Read full content

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

Use case: When you want to load the whole file into memory.

✅ Example 2: Read partial content

with open("data.txt", "r") as file:
    partial = file.read(10)  # Reads first 10 characters
    print(partial)

Use case: When you only need a portion of the file.

📘 2. readline( )

Reads one line at a time from the file.

✅ Example 1: Read first line

with open("data.txt", "r") as file:
    first_line = file.readline()
    print(first_line)

Use case: Useful for headers or line-by-line processing.

✅ Example 2: Loop through lines

with open("data.txt", "r") as file:
    line = file.readline()
    while line:
        print(line.strip())
        line = file.readline()

Use case: Efficient for large files where memory is a concern.

📘 3. readlines( )

Reads all lines and returns them as a list of strings.

✅ Example 1: Read all lines into a list

with open("data.txt", "r") as file:
    lines = file.readlines()
    print(lines)

Use case: When you want to process each line individually later.

✅ Example 2: Iterate over list of lines

with open("data.txt", "r") as file:
    for line in file.readlines():
        print(line.strip())

Use case: Clean and readable way to loop through file content.

Each method has its strengths:

• read() is great for small files.

• readline() is ideal for streaming or large files.

• readlines() is handy when you want a list of lines.

Functions to Write into Text Files in Python

To write data to text files in Python, you typically use the open() function with a write mode ('w', 'a', or 'w+') and then use methods like write() or writelines() to insert content. Here’s a breakdown with three examples each for the most common writing methods:

✍️ 1. write() Method

Writes a single string to the file.

✅ Example 1: Overwrite with a single line

with open("example1.txt", "w") as file:
    file.write("Hello, world!\n")

✅ Example 2: Append a new line

with open("example1.txt", "a") as file:
    file.write("This is an appended line.\n")

✅ Example 3: Write multiple lines one by one

with open("example1.txt", "w") as file:
    file.write("Line 1\n")
    file.write("Line 2\n")
    file.write("Line 3\n")

📋 2. writelines() Method

Writes a list of strings to the file.

✅ Example 1: Write a list of lines

lines = ["First line\n", "Second line\n", "Third line\n"]
with open("example2.txt", "w") as file:
    file.writelines(lines)

✅ Example 2: Append multiple lines

more_lines = ["Fourth line\n", "Fifth line\n"]
with open("example2.txt", "a") as file:
    file.writelines(more_lines)

✅ Example 3: Write lines from a loop

data = [f"Item {i}\n" for i in range(1, 4)]
with open("example2.txt", "w") as file:
    file.writelines(data)

🧪 3. Using print() with file argument

A lesser-known but handy way to write to files.

✅ Example 1: Print to file

with open("example3.txt", "w") as file:
    print("Printed line using print()", file=file)

✅ Example 2: Print multiple lines

with open("example3.txt", "w") as file:
    for i in range(3):
        print(f"Line {i+1}", file=file)

✅ Example 3: Append with print

with open("example3.txt", "a") as file:
    print("Appended with print()", file=file)

Each method has its own strengths:

• write() is precise and good for single strings.

• writelines() is efficient for lists.

• print() is flexible and auto-adds newline characters.