[Python-Dev] Decimal - context manipulation (original) (raw)

Tim Peters tim.one at comcast.net
Wed Apr 21 12:13:16 EDT 2004

[Batista, Facundo]

... Regarding a copy() method in Context class, don't know. It's really easy to implement, but don't know if the standard preference is to get a copy method inside each data type (I'm confused about dictionaries having a copy method and lists, for example, not having it).

There have always been several succinct ways to get a (shallow) copy of a list, like

copied_list = list(original)

and

copied_list = original[:]

For dicts, while you can do

copied_dict = dict(original)

today, at the time dict.copy() was introduced you could not do that.

I usually add a .copy() method to my mutable types, like so:

class MyClass: ... def copy(self): return build_a_shallow_copy_of(self) copy = copy

Note that copy is a special name, and the standard copy.copy(thing) automatically invokes thing.copy() if thing has a copy() method. The "copy = copy" line then supplies that method directly to class users too under a conventional name. So, after the above, copy.copy(thing) and thing.copy() both work.

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