Tracking the number of recursive calls without using global variables in Python

Question

How to track the number of recursive calls without using global variables in Python. For example, how to modify the following function to keep track the number of calls?

def f(n):
    if n == 1:
        return 1
    else:
        return n * f(n-1)

print f(5)

Answer 1

Here's a neat trick that doesn't use a global: you can stash the counter in the function itself.

def f(n):
    f.count += 1
    if n == 1:
        return 1
    else:
        return n * f(n-1)

After which:

>>> f.count = 0 # initialize the counter
>>> f(5)
120
>>> f.count
5
>>> f(30)
265252859812191058636308480000000L
>>> f.count
35

This handles the "all calls ever" case, anyhow.

Answer 2

As delnan said, if you want all calls ever, it's impossible without a global, so I'm assuming you just want the call depth, for which you just need to add a return value

def f(n):
    if n == 1:
        return 1,0
    else:
        x, call_depth= f(n-1)
        return n * x, call_depth+1

If you're dealing with several recursive calls, you can do a max(call_depth1, call_depth2) (depth of longest call tree) or just sum the two (total number of actual calls)