PCEP Practice Question: Functions, Tuples, Dictionaries and Exceptions
A developer writes a function `def log_event(message, level='INFO'):` that appends a formatted string to a list. The developer calls `log_event('disk full')` and then `log_event('retrying', level='WARN')`. What is the result of these two calls?
⚠ Common exam trap
The trap here is believing that passing a keyword argument in one call rewrites the function's default, when defaults are fixed at definition time and merely overridden per call.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The first call uses 'INFO' for level and the second uses 'WARN', because the default applies only when the argument is omitted.
Default arguments make a parameter optional and are bound only when the caller omits that argument. An explicit keyword argument replaces the default for that single call without changing the function's definition, so the first invocation logs at INFO and the second at WARN. Calls that mix positional and keyword arguments are valid when each parameter is filled once.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The first call uses 'INFO' for level and the second uses 'WARN', because the default applies only when the argument is omitted.
Why this is correct
Default parameter values are used only when the caller does not supply that argument. The first call omits level, so the default 'INFO' is bound; the second call passes level explicitly by keyword, which overrides the default with 'WARN'. Both calls succeed and produce the intended log entries for the developer.
- ✗
The first call raises a TypeError because a function with a default parameter must always receive that argument explicitly.
Why it's wrong here
A parameter with a default is optional by definition; omitting it is exactly the situation the default exists to handle. The call `log_event('disk full')` binds message to the string and level to 'INFO'. No error occurs, and the function can be invoked with a single argument whenever the default severity is acceptable.
- ✗
The second call raises a TypeError because positional and keyword arguments cannot be mixed in the same call.
Why it's wrong here
Python allows mixing positional and keyword arguments as long as no argument receives a value twice. The call `log_event('retrying', level='WARN')` supplies message positionally and level by keyword, which is perfectly valid. A TypeError would arise only if message were also passed by keyword after being filled positionally.
- ✗
Both calls use 'WARN', because the second call permanently changes the default for later invocations.
Why it's wrong here
Assigning an argument in one call has no effect on the function's default value; defaults are evaluated once at function definition time and remain fixed unless the function object itself is modified. The first call therefore still receives 'INFO'. Only mutable default objects can be accidentally shared, and rebinding a parameter name is not that case.
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Last reviewed September 2026 · checked against the official Python Institute exam blueprint
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