Troubleshooting & Problem Resolution Flashcards

A `StopIteration` exception propagates out of a generator function unexpectedly. What Python version behavior causes this?

Answer: In Python 3.7+, StopIteration raised inside a generator is converted to RuntimeError

PEP 479 (active from Python 3.7) converts `StopIteration` raised inside a generator body into a `RuntimeError` to prevent silent bugs.

You profile a slow script with `cProfile` and find most time is spent in a pure-Python loop. What is the best optimization?

Answer: Replace the loop with a NumPy vectorized operation or a built-in written in C

NumPy operations and built-in functions execute compiled C code, which is orders of magnitude faster than pure-Python loops.

You get `ssl.SSLCertVerificationError` when making an HTTPS request. What is the secure resolution?

Answer: Update the CA certificates bundle used by Python or the requests library

Updating the CA bundle ensures Python can validate the server's certificate chain without disabling security.

A long-running script leaks memory over time. `tracemalloc` shows many small string allocations in a loop. What is a likely culprit?

Answer: String concatenation with `+` inside a loop, creating a new object each iteration

Each `+` on strings creates a new immutable string object; accumulation inside a loop grows memory linearly.

A subprocess call with `subprocess.run(['ls', '-l'])` works locally but raises `FileNotFoundError` on Windows. Why?

Answer: `ls` is a Unix command not available on Windows; use `dir` with `shell=True` on Windows

`ls` is a Unix shell command; Windows uses `dir`, and since it is a shell built-in, `shell=True` is required.

You add `print` statements to debug, but output is not visible when piping the script's stdout. What causes this?

Answer: Python buffers stdout when writing to a pipe; use flush=True or set PYTHONUNBUFFERED=1

Python uses block buffering for stdout when it detects a pipe, so output may not appear until the buffer is flushed.

A class method decorated with `@staticmethod` raises `TypeError: method() takes 0 positional arguments but 1 was given`. What went wrong?

Answer: The decorator was removed or misapplied, so Python is passing `self` to what should be a static method

Without `@staticmethod`, Python treats the method as an instance method and automatically passes `self` as the first argument.