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Exception Handling

Context Managers

Resource management with the with statement

Interview: Pythonic resource handling — tests understanding of __enter__/__exit__, contextlib, and resource safety

Last Updated: June 12, 2026 • 7 min read

Context managers ensure that resources are properly acquired and released, even when exceptions occur. The with statement is the most Pythonic way to manage files, connections, locks, and any resource that needs cleanup. They're implemented via the __enter__/__exit__ protocol or the contextlib module.

How Context Managers Work

  • __enter__(): Called when entering the with block (setup)
  • __exit__(exc_type, exc_val, exc_tb): Called when leaving (cleanup)
  • If __exit__ returns True, exceptions are suppressed
  • If __exit__ returns False or None, exceptions propagate

contextlib Module

  • @contextmanager: Create context managers from generator functions
  • ExitStack: Manage multiple context managers dynamically
  • suppress(): Ignore specific exceptions

Interview Tip

Know the difference between class-based and generator-based context managers. Also understand when __exit__ should return True (suppress exception) vs False (propagate).

Use Cases

File handling: automatic close even on exceptions

Database transactions: commit on success, rollback on failure

Lock management: acquire/release thread/process locks

Temporary resources: files, directories, network connections

Timing/profiling: measure execution time of code blocks

Common Mistakes

Forgetting to yield in @contextmanager generator (must yield exactly once)

Not handling exceptions in __exit__ (cleanup must work even on errors)

Returning True from __exit__ accidentally (suppresses exceptions silently)

Using context managers when simple try/finally would be clearer

Not understanding that the value after