Defining and Calling Functions
Try it: Defining and Calling Functions
What def and a call really do: def only creates a function object, a call binds the arguments to the parameters in a new frame and runs the body, return ends the call at once and its value replaces the call expression in the caller — while a function that only prints gives back None.
How it works
- def name(params): creates a function object and binds the name to it; the body does not run yet.
- A call evaluates its arguments, opens a new frame, binds each parameter to its argument and runs the body from the top.
- return value ends the call immediately (lines after it never run) and sends the value back; the frame and its local names are discarded.
- In the caller, the call expression is replaced by the returned value, which can be stored, used in a larger expression or passed to another call.
- A body that ends without return (e.g. one that only prints) makes the call evaluate to None — so x = f() stores None and None + 1 raises TypeError.
- Calling a name before its def has run raises NameError: the function does not exist yet.
Default run (18 steps): The program is ready. Python runs it from the top, one statement at a time. Idea: the value a call returns is what the caller stores. … The program finished. Console: 8.
Simplified: Four fixed, hand-written programs; you edit the literal arguments, switch the body between return and print, and move the def after the calls. The lab's own small evaluator runs them (your input is never executed as code); every variant was run in CPython 3.12 and the lab reproduces its sys.settrace line/call/return/exception events, its output and its error message. Functions are shown as <function name> without a memory address.
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