Raymond Hettinger wrote:
Use copy.copy() for generic copying -- it works across a wide range
objects. Alternatively, use the constructor as generic way to make duplicates:
dup = set(s) dup = list(l) dup = dict(d) dup = tuple(t) # note, the duplicate is original object here
I know all this, but why then is there a copy method for sets and dictionaries? What justification is valid for sets and dictionaries that doesn't apply to lists?
* maybe it's a Dutch thing;
* dict.copy() pre-dated dict(d) and (IIRC) copy.copy();
* sets and dicts don't have the [:] syntax available to them;
* the __copy__() method is new way to make things copy.copyable without fattening the apparent API or rewriting the copy module;
* because generic copying isn't important enough to add more ways to do the same thing;
* and because Guido believes beginners tend to copy too much (that is one reason why copy.copy is not a builtin) and that the language should encourage correct behavior.