Nick Mellor wrote: > Hi guys, > > (Python 2.7, Windows 7 64-bit) > > Here's a bit of code stress-testing a method addUpdate_special_to_cart. > The test adds and updates random "specials" (multiple products bundled at > an advantageous price) of various sizes to thousands of shopping carts, > then restocks the whole darn lot. The test passes if the stock level > afterwards is the same as it was before executing the code for all > products. > > addUpdate_special_to_cart is working perfectly. But the test isn't. > > The test iterates over the same code twice, once with special_qty==4, once > with special_qty==0, reseeding the Python random module number generator > to a fixed seed (a string) between the iterations. special_qty==0 removes > the special and restocks the products. The test relies on precisely the > same random number sequence on both runs. > > Can you think of a reason why the random number generator should fall out > of sync between the two iterations? Because that's what's happening by the > look of it: occasionally products are returned to the wrong stockbin. No > "random" module method is used anywhere else while this code is executing. > > When I assign something non-random to the stockbin parameter, the test > passes. > > Best wishes, > > > > Nick > > for qty in [4, 0]: > random.seed(seed) > for cart in range(test_size): > for special in range(randrange(3)): > s.addUpdate_special_to_cart(cart=cart, > stockbin=randrange(test_size), > special_id=randrange(test_size), > special_qty=qty, > products=[(random.choice(PRODUCTS), > random.choice(range(10))) > for r in > range(randrange(7))])
An exotic option: I notice that randrange() is the only random function not qualified with the module name. If you are using a fancy auto-reloading web framework things can get out of sync: >>> import random >>> from random import randrange >>> random.seed(42) >>> [randrange(10) for _ in range(5)] [6, 0, 2, 2, 7] >>> random.seed(42) >>> [randrange(10) for _ in range(5)] [6, 0, 2, 2, 7] >>> reload(random) <module 'random' from '/usr/lib/python2.7/random.pyc'> >>> random.seed(42) >>> [randrange(10) for _ in range(5)] [6, 8, 0, 4, 0] -- https://mail.python.org/mailman/listinfo/python-list
