Comparison of LBYL versus EAFP

gistfile1.py

# Comparison of LBYL versus EAFP
# http://www.reddit.com/r/Python/comments/pou99/python_performance_tips_part_1/
from __future__ import print_function
from hashlib import md5


_lbyl_cache = {}
_eafp_cache = {}


def calculation(x):
    """Does an 'expensive' calculation with the input."""
    return md5(str(x).encode('ascii')).hexdigest()
    

def lbyl(x):
    """Look before you leap strategy."""
    if x not in _lbyl_cache:
        _lbyl_cache[x] = calculation(x)
    return _lbyl_cache[x]


def eafp(x):
    """Easier to ask forgiveness than permission strategy."""
    try:
        return _eafp_cache[x]
    except KeyError:
        _eafp_cache[x] = calculation(x)
        return _eafp_cache[x]


def test1(func):
    """Many repeated values, would benefit from memo-ization."""
    for x in range(200):
        func(x % 5)

    flush()
    

def test2(func):
    """Unique values, defeats memo-ization."""
    for x in range(200):
        func(x)
    
    flush()


def flush():
    global _lbyl_cache
    global _eafp_cache
    
    _lbyl_cache = {}
    _eafp_cache = {}

        

if __name__ == "__main__":
    import timeit
    
    setup = 'from __main__ import test1, test2, lbyl, eafp'
    n = 10000
    
    print('Memo-ization friendly test') 
    t1 = timeit.repeat('test1(lbyl)', setup, number=n)
    t2 = timeit.repeat('test1(eafp)', setup, number=n)
    print('LBYL', t1)
    print('EAFP', t2)
    print('Difference', min(t1) / min(t2))
    
    print('Memo-ization un-friendly test')
    t1 = timeit.repeat('test2(lbyl)', setup, number=n)
    t2 = timeit.repeat('test2(eafp)', setup, number=n)
    print('LBYL', t1)
    print('EAFP', t2)
    print('Difference', min(t1) / min(t2))