Mr.Rech <[EMAIL PROTECTED]> wrote: ... > Suppose one of the attributes of my class is a dictionary whose values > are callable functions, such as: > > >>>def foo(): > ..... pass > >>>def bar(): > ..... pass > > >>>adict = dict(a = foo, b = bar) > > Now if I try: > > >>> anotherdict = copy.deepcopy(adict) # It doesn't work
Right, because functions are not copyable (although you could, if you wished, write a way to copy them and copy_reg it). > however: > > >>> anotherdict = copy.copy(adict) # works as expected Right, as it's a shallow copy. > My question is: anotherdict is really a copy of adict? If so, what is > the difference between its definition and the following: > > >>> yanotherdict = dict(adict) No difference whatsoever, and in fact >>> guesswhat = adict.copy() is yet another way to do just the same thing -- a shallow copy. The use of copy.copy(foo) is recommended when you aren't sure what type you're dealing with in 'foo', but want the same identical type as a result; the use of dict(foo) is recommended when you aren't sure what type you're dealing with in 'foo', but want a dict as a result. If you're certain you're dealing with a dict, then, if this code is critical for your app's performance, pick the fastest way. Use timeit to find the fastest way, e.g., on my iBook: Helen:~ alex$ python -mtimeit -s'd=dict.fromkeys(range(99))' -s'import copy' 'copy.copy(d)' 100000 loops, best of 3: 17.3 usec per loop Helen:~ alex$ python -mtimeit -s'd=dict.fromkeys(range(99))' -s'import copy' 'd.copy()' 100000 loops, best of 3: 11.4 usec per loop Helen:~ alex$ python -mtimeit -s'd=dict.fromkeys(range(99))' -s'import copy' 'dict(d)' 100000 loops, best of 3: 12.8 usec per loop Helen:~ alex$ I would avoid copy.copy (measurably slower) and end up using (as I usually do...) dict(d), but I wouldn't bitch against anybody choosing to use d.copy() instead for a 10%-or-so gain in speed. Personally, I find that list(L), dict(D), set(S) and so on are the best way to perform shallow copies for known-type objects, and strongly dislike type-specific divergences such as L[:] and D.copy() and S.copy(), but there's no community consensus on this point. Alex -- http://mail.python.org/mailman/listinfo/python-list
