1. The Problem with Manual Closing

In the previous lessons, we always had to remember to call file.close(). But what if an error occurs before we reach that line?

file = open("data.txt", "r")
content = file.read()
result = 10 / 0      # This causes an error!
file.close()            # This line NEVER runs!

If an error occurs between open() and close(), the file stays open. Open files consume system resources and can prevent other programs from accessing the file. The with statement solves this problem.

2. The with Statement

The with statement automatically closes the file when the block ends, even if an error occurs:

# The file is automatically closed when the block ends
with open("greeting.txt", "r") as file:
    content = file.read()
    print(content)

# File is now closed - no need to call file.close()
print("File is closed:", file.closed)  # True

with open("output.txt", "w") as file:
    file.write("Line 1\n")
    file.write("Line 2\n")
    file.write("Line 3\n")
# File is automatically saved and closed here

3. Why with Is Better

Compare the two approaches:

# You have to remember to close
file = open("data.txt", "r")
try:
    content = file.read()
    # process content...
finally:
    file.close()  # Ensure file closes even if error

# Cleaner, safer, and automatic
with open("data.txt", "r") as file:
    content = file.read()
    # process content...
# File is automatically closed

The with statement is preferred because it is:

• Safer: The file closes even if an error occurs
• Cleaner: Less code to write
• Clearer: It is obvious where the file is being used

4. Common Patterns with the with Statement

with open("scores.txt", "r") as file:
    for line in file:
        name, score = line.strip().split(": ")
        print(f"{name} scored {score}")

with open("names.txt", "r") as file:
    names = [line.strip() for line in file]

# The list is available after the with block
print(f"Found {len(names)} names")
print(names)

with open("journal.txt", "a") as file:
    entry = input("Today's journal entry: ")
    file.write(entry + "\n")
    print("Entry saved!")

5. Working with Multiple Files

You can open multiple files in a single with statement or nest them:

# Open two files at once
with open("source.txt", "r") as source:
    with open("backup.txt", "w") as backup:
        for line in source:
            backup.write(line)

print("Backup complete!")

# Copy only lines that contain "error"
with open("app.log", "r") as log_file:
    with open("errors.log", "w") as error_file:
        for line in log_file:
            if "error" in line.lower():
                error_file.write(line)