deepcopy can't handle custom metaclasses

[glchapman]

BPO	560794
Nosy	@gvanrossum
Files	copy.py.diff copy.py.diff

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/gvanrossum'
closed_at = <Date 2002-06-10.21:10:39.000>
created_at = <Date 2002-05-26.19:15:21.000>
labels = ['library']
title = "deepcopy can't handle custom metaclasses"
updated_at = <Date 2002-06-10.21:10:39.000>
user = 'https://bugs.python.org/glchapman'

bugs.python.org fields:

activity = <Date 2002-06-10.21:10:39.000>
actor = 'gvanrossum'
assignee = 'gvanrossum'
closed = True
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2002-05-26.19:15:21.000>
creator = 'glchapman'
dependencies = []
files = ['494', '495']
hgrepos = []
issue_num = 560794
keywords = []
message_count = 3.0
messages = ['10933', '10934', '10935']
nosy_count = 2.0
nosy_names = ['gvanrossum', 'glchapman']
pr_nums = []
priority = 'normal'
resolution = 'accepted'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue560794'
versions = ['Python 2.2']

[glchapman]

This is essentially the same problem as that reported in
bug 494904 for pickle: deepcopy should treat instances
of custom metaclasses the same way it treats
instances of type 'type'. I've attached a provisional fix
which is basically a copy of the patch made to pickle (it
checks to see if the type of the thing being deepcopied
is a subclass of type).

One question: it seems to me that the exception
handling code is unnecessary both here and in the
pickle module. In both cases, the first parameter to
subclass is the result of a call to 'type' and the second
is type 'type' itself, so it doesn't seem like there's any
reason to worry about a TypeError.

[glchapman]

Logged In: YES
user_id=86307

I changed the patch so that issubclass is called before the
attempt to access __deepcopy__ (to avoid unbound instance
method problem methioned in 494904).

[gvanrossum]

Logged In: YES
user_id=6380

Thanks; I've checked this in. For the reason of the except
clause, see python.org/sf/502085.