Op 2004-12-16, Fredrik Lundh schreef <[EMAIL PROTECTED]>: > Antoon Pardon wrote: > >> That depends on whether the programmes wants value equality >> or identity equality. >> >> In the first case the programmer shouldn't mutate a after >> it was introduced as key in the dictionary; but should >> either introduce a copy or work on a copy later. As >> such your snippet of code would become. >> >> a = [1,2,3] >> d[a[:]] = 9 >> a.append(4) >> print d[a] >> >> And this would raise a KeyError, unless the list [1,2,3,4] >> would be in the dictionary. >> >> In the second case your code would produce 9. > > how does the dictionary know if you want key value equality or key > identity equality?
By the __hash__ and __eq__ methods you provide on your object. -- Antoon Pardon -- http://mail.python.org/mailman/listinfo/python-list
