Lesson 58: Context Managers

Introduction to Context Managers

Context managers are Python objects that manage resources using the with statement. They ensure proper setup and cleanup of resources, like files, automatically. Context managers make code cleaner and prevent resource leaks.

The with statement is the most common way to use context managers, especially for file operations.

Using with Statement

The with statement automatically handles resource management:

with_statement.py
# File handling with context manager
with open("file.txt", "w") as file:
    file.write("Hello, World!")
# File is automatically closed here

# Reading with context manager
with open("file.txt", "r") as file:
    content = file.read()
    print(content)
# File automatically closed

# Multiple context managers
with open("input.txt", "r") as infile, open("output.txt", "w") as outfile:
    data = infile.read()
    outfile.write(data.upper())

Creating Custom Context Managers

You can create your own context managers using classes:

custom_context.py
class Timer:
    def __enter__(self):
        import time
        self.start = time.time()
        return self
    
    def __exit__(self, exc_type, exc_val, exc_tb):
        import time
        elapsed = time.time() - self.start
        print(f"Elapsed time: {elapsed:.2f} seconds")

# Use custom context manager
with Timer():
    # Some code here
    sum(range(1000000))

Benefits of Context Managers

Context managers provide several advantages:

Automatic resource cleanup
Exception-safe resource handling
Cleaner, more readable code
Prevents resource leaks
Standard pattern for resource management

Best Practices

✅ Context Manager Tips

• Always use with for file operations

• Context managers ensure cleanup even if errors occur

• Use contextlib module for simpler context managers

• Context managers are essential for proper resource management

• Prefer context managers over manual cleanup