Different ways of fib() in Python

fibs.py

N=30
PRINT = False

def f1(n):
    if n < 2: return n
    return f1(n-1) + f1(n-2)
print f1(N) if PRINT

def f2(n, mem={}):
    if n < 2: return n
    r = mem.get(n, f2(n-1, mem) + f2(n-2, mem))
    mem[n] = r
    return r
print f2(N) if PRINT

def f3(n, mem):
    mem[0] = 0
    mem[1] = 1
    for i in range(2, n+1):
        mem[i] = mem[i-1] + mem[i-2]
    return mem[n]
print f3(N, [0]*(N+1)) if PRINT

def f4(n):
    i, j = 0, 1
    
    for _ in range(n-1):
        i, j = j, i+j
    return j
print f4(N) if PRINT