Understanding and visualizing recursion

Theres a python module for that

Generated with:

from rcviz import callgraph, viz
st= []
@viz
def combi(prefix, s):
    if len(s)==0: 
        return 
    else:
        st.append(prefix+s[0])     
        combi.track(st = st) #track st in rcviz 
        combi(prefix+s[0],s[1:])
        combi(prefix,s[1:])
        return st

print combi("",'abc')
callgraph.render("combi.png")

There are two recursive calls to combi() in the function. Thus the path of calls is not a single line, but rather a binary tree that forks. What you are seeing is the second half of the tree.

I drew the recursion tree. By Depth First Traversal, the final output is got at the last node. This visualization helps understand what's happening.