POC Cheat Sheet 2026

The 30 highest-yield POC facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. What does the `seek(0)` method do on a file object? → Moves the file pointer to the beginning
2. Which Python function sends an HTTP GET request when using the `requests` library? → requests.get()
3. How do you add an item to a list in Python? → list.append(item)
4. Which HTTP method is used to retrieve data from a server without modifying state? → GET
5. Which module is commonly used for debugging in Python? → pdb
6. What role does documentation play in system architecture? → It enables team understanding, maintenance, and future development decisions
7. What is the 80/20 rule as applied to performance optimization? → 80% of performance gains come from optimizing 20% of the code or configuration
8. What does the traceback module provide? → Error traceback information
9. In Python's `requests` library, how do you pass query string parameters in a GET request? → Using the `params` keyword argument with a dictionary
10. What decorator is used in unittest to mark a test that should be skipped? → @unittest.skip
11. What does `if __name__ == '__main__':` guard protect against? → Running top-level code when the module is imported by another module
12. What is the output of `'abc' * 3`? → 'abcabcabc'
13. What is the purpose of verifying a fix after implementation? → To confirm the solution resolved the issue without creating new problems
14. Which method would you call on a `prometheus_client.Counter` object to increment it by a custom amount? → .inc(n)
15. In Python, which module is used to run external shell commands and capture their output? → subprocess
16. Which approach correctly reads a value from an environment variable with a fallback default in Python? → os.environ.get('KEY', 'default')
17. How do you check for syntax errors in Python? → Using a linter or running the code
18. What is the purpose of the `nonlocal` keyword? → It allows an inner function to modify a variable in an enclosing (non-global) scope
19. What does the 'melt()' function in pandas accomplish? → Unpivots a wide DataFrame into a long format
20. Why is data validation important during integration? → It ensures data accuracy and consistency across connected systems
21. Which Python keyword is used to define an anonymous function? → lambda
22. Which Python standard library module is used to read and write JSON data? → json
23. In Selenium WebDriver automation, which method waits up to a maximum time for a condition to be true before throwing a TimeoutException? → WebDriverWait(driver, timeout).until(condition)
24. Which `pytest` plugin is used to measure code coverage during test runs and integrates with the `coverage.py` tool? → pytest-cov
25. What HTTP status code indicates a successful request? → 200
26. What is the difference between `__repr__` and `__str__`? → `__repr__` is for developers (unambiguous), `__str__` is for end-users (readable)
27. You add `print` statements to debug, but output is not visible when piping the script's stdout. What causes this? → Python buffers stdout when writing to a pipe; use flush=True or set PYTHONUNBUFFERED=1
28. When designing a Python system that must handle millions of events per second, which architecture pattern is most appropriate? → Event-driven architecture with message streaming
29. What does the 'pivot_table()' function in pandas do? → Creates a spreadsheet-style pivot table as a DataFrame
30. Which Python tool is the standard for measuring code coverage during testing? → coverage.py