SHARK_PRO

🔰 What Is File Handling?

🟢 Lesson 3

File handling lets your Python programs interact with files on your computer — read data from them or save data to them.

📁 You can:

• 🔍 Read data from files (like .txt, .csv)
• ✏️ Write or append new data
• 🗂️ Use it to store logs, user input, or application data

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📘 Basic Syntax: open()

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

Mode	Purpose
'r'	Read (default)
'w'	Write (overwrite file)
'a'	Append (add to file)
'x'	Create a new file (error if exists)
'b'	Binary mode
't'	Text mode (default)

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📖 Reading a File

✅ Method 1: Using open() and read()

pythonCopierModifierfile = open("example.txt", "r")
content = file.read()
print(content)
file.close()

📌 Important: Always close() the file when done.

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✅ Method 2: Using with (recommended)

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

✔ with automatically closes the file when finished.

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✍️ Writing to a File

pythonCopierModifierwith open("output.txt", "w") as file:
    file.write("Hello from Python!\n")
    file.write("This will overwrite the file.")

📌 'w' mode creates a new file or overwrites an existing one.

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➕ Appending to a File

pythonCopierModifierwith open("output.txt", "a") as file:
    file.write("\nThis line was added later.")

📌 'a' mode keeps existing content and adds new lines.

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🔄 Reading Line by Line

pythonCopierModifierwith open("example.txt", "r") as file:
    for line in file:
        print("🔹", line.strip())

✔ strip() removes newlines and extra spaces.

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🧠 Exercise 1: Write and Read

1. Ask the user to enter 3 lines.
2. Save them to notes.txt.
3. Then read and display the file content.

pythonCopierModifierwith open("notes.txt", "w") as file:
    for i in range(3):
        line = input(f"Enter line {i+1}: ")
        file.write(line + "\n")

print("\n📄 File Contents:")
with open("notes.txt", "r") as file:
    print(file.read())

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🧠 Exercise 2: Count Lines in a File

Assume a file students.txt exists. Count how many lines it contains.

pythonCopierModifierwith open("students.txt", "r") as file:
    lines = file.readlines()

print("📋 Total lines:", len(lines))

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🛠 Tip: Handle Missing Files Gracefully

pythonCopierModifiertry:
    with open("missing.txt", "r") as file:
        print(file.read())
except FileNotFoundError:
    print("❌ File not found.")

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📝 Summary

• Use open("file", "mode") to access files.
• Always use with open(...) to handle files safely.
• Modes like 'r', 'w', 'a' define how the file is opened.
• Use .read(), .write(), and .readlines() to manipulate content.

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