18.9: Stack Diagrams for Recursive Functions
- Page ID
- 16952
In Section 3.10, we used a stack diagram to represent the state of a program during a function call. The same kind of diagram can help interpret a recursive function.
Every time a function gets called, Python creates a new function frame, which contains the function’s local variables and parameters. For a recursive function, there might be more than one frame on the stack at the same time.
Figure 5.9.1 shows a stack diagram for countdown
called with n = 3
.

As usual, the top of the stack is the frame for __main__
. It is empty because we did not create any variables in __main__
or pass any arguments to it.
The four countdown
frames have different values for the parameter n
. The bottom of the stack, where n=0
, is called the base case. It does not make a recursive call, so there are no more frames.
Exercise \(\PageIndex{1}\)
Draw a stack diagram for print_n
called with s = 'Hello'
and n=2
.
Exercise \(\PageIndex{2}\)
Write a function called do_n
that takes a function object and a number, n, as arguments, and that calls the given function n
times.