📖 File Fundamentals — Opening and Closing Files

Learn the basics of working with files: opening them, reading/writing data, and closing them properly.

🎯 Opening Files

Use the `open()` function to work with files. It requires a filename and mode.

# Open a file for reading (default mode)
file = open("data.txt", "r")

# Do something with the file
content = file.read()

# Always close the file
file.close()

File Modes:

• `"r"` — Read (default, file must exist)

• `"w"` — Write (creates new or overwrites existing)

• `"a"` — Append (adds to end of file)

• `"x"` — Create (fails if file exists)

• `"b"` — Binary mode (combine with others: `"rb"`, `"wb"`)

💡 Why Closing Matters

Closing files releases system resources and ensures all data is saved.

# Open for writing
file = open("output.txt", "w")
file.write("Hello, World!")
file.close()  # Must close to save data!

# Without close, file might not be fully written
file = open("output.txt", "w")
file.write("Hello")
# File not closed - data might be lost!

🎨 Real-World Example: Reading a Log File

# Open a log file for reading
log_file = open("application.log", "r")

# Read entire file as string
content = log_file.read()
print(content)

# Close when done
log_file.close()

📊 File Object Operations

🔑 Key Takeaways

• ✅ Use `open(filename, mode)` to open files

• ✅ Modes: `"r"` read, `"w"` write, `"a"` append

• ✅ Always `close()` files after use

• ✅ Closing releases resources and saves data

• ✅ File must exist for `"r"` mode

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