Showing that try/except is slower than isinstance

tryexcept_vs_isinstance.py

'''
Example showing that isinstance checks are faster than doing a "it's better to ask for forgiveness than
permission approach.
'''

from timeit import Timer

# Silly timing code that can be ignored
def timeruns(runs, num_iterations = 100):
    return [(label, Timer(cmd, imports).timeit(num_iterations))
      for cmd, imports, label in runs]

def format_runs(runresults):
    result = "Timing Results:\n%s\n" % ("-" * 20)
    minlabel, mintime = "Arbitrary label", 12319283719827319.0
    maxlabel, maxtime = "Arbitrary label", -1.0
    for label, time in runresults:
        result += "%s : %s\n" % (label, time)
        if time < mintime:
            mintime = time
            minlabel = label
        if time > maxtime:
            maxtime = time
            maxlabel = label

    result += "%s\n" % ("-" * 20)
    per_faster = round((1.0 - mintime / maxtime) * 100)

    result += ("Fastest time: %s - %s (%s%% faster than slowest)\n" %
               (minlabel, mintime, per_faster))
    result += "Slowest time: %s - %s\n" % (maxlabel, maxtime)
    return result


# Do an eq using try/except on AttributeError
class Foo(object):
    def __init__(self, val):
        self.val = val
    def __eq__(self, other):
        try:
            return other.val == self.val
        except AttributeError:
            return NotImplemented

# Do an eq using a simple isinstance check
class Bar(object):
    def __init__(self, val):
        self.val = val
    def __eq__(self, other):
        if isinstance(other, Bar):
            return other.val == self.val
        return NotImplemented

if __name__ == "__main__":
    setup = """
from __main__ import Foo, Bar
f = Foo(42)
b = Bar(42)
"""
    num_iter = 1000000
    runs = [("f == '42kldfj'", setup, "doing exception"),
            ("b == '42kldfj'", setup, "doing isinstance")]
    print(format_runs(timeruns(runs, num_iter)))