recursion-example.py

#!/usr/bin/env python3
from __future__ import print_function


def f(n, level=0):
    indent = level * '    '
    print(indent, 'start', n)
    if n == 10202:
        print(indent, 'return constant from', n)
        return 4
    re = f(n ** 2 + 1, level + 1)
    print(indent, 'continue', n)
    s = 2 * n * re
    print(indent, 's =', s)
    print(indent, 'return from', n)
    return s

f(3)

# start 3
#     start 10
#         start 101
#             start 10202
#             return constant from 10202
#         continue 101
#         s = 808
#         return from 101
#     continue 10
#     s = 16160
#     return from 10
# continue 3
# s = 96960
# return from 3