Re: [Python-Dev] Possible wrong behavior of the dict?
On Tue, Mar 17, 2015 at 3:46 PM Zaur Shibzukhov szp...@gmail.com wrote:
So in such cases it should not subclassed `dict`, but
`collections.MutableMapping`, for example?
Yes (see the comment at
https://hg.python.org/cpython/file/22a0c925a7c2/Objects/dictobject.c#l2003
).
-Brett
---
*Zaur Shibzukhov*
2015-03-17 22:38 GMT+03:00 Brett Cannon br...@python.org:
On Tue, Mar 17, 2015 at 3:29 PM Zaur Shibzukhov szp...@gmail.com wrote:
Yes... But I expected that dict constructor will use `__getitem__` or
`items` method of MyDict instance in order to retrieve items of the MyDict
instance during construction of the dict instance... Instead it interpreted
MyDict instance as the dict instance during construction of new dict.This
exactly caused my confusion.
It's because you subclassed dict. Copying is optimized to skip over using
the methods you listed when the object is a dict and so we know the
structure of the object at the C level. You can look at
https://hg.python.org/cpython/file/22a0c925a7c2/Objects/dictobject.c#l1997
to see the actual code.
-Brett
---
*Zaur Shibzukhov*
2015-03-17 22:12 GMT+03:00 Brett Cannon br...@python.org:
On Tue, Mar 17, 2015 at 3:05 PM Zaur Shibzukhov szp...@gmail.com
wrote:
Hello!
In order to explain, let define subclass of dict:
class Pair:
def __init__(self, key, val):
self.key = key
self.val = val
class MyDict(dict):
#
def __init__(self, *args, **kwds):
if len(args) 1:
raise TypeError('Expected at most 1 arguments, but got %d'
% len(args))
for key, val in args[0]:
self[key] = val
for key, val in kwds.items():
self[key] = val
def __getitem__(self, key):
pair = dict.__getitem__(key)
return pair.value
def __setitem__(self, key, val):
if key in self:
pair = dict.__getitem__(key)
pair.value = value
else:
pair = Pair(key, val)
dict.__setitem__(self, key, pair)
def values(self):
for key in self:
p = dict.__getitem__(self, key)
yield p.value
def items(self):
for key, p in dict.__iter__(self):
yield p.key, p.value
The simple test give me strange result:
d = MyDict([('a', 1), ('b', 2), ('c', 3)])
dict(d)
{'a': __main__.Pair at 0x104ca9e48,
'b': __main__.Pair at 0x104ca9e80,
'c': __main__.Pair at 0x104ca9eb8}
instead of {'a':1, 'b':2, 'c':3}.
Is this right behavior of the dict?
Yes because in your __setitem__ call you are storing the value as the
Pair. So when dict prints its repr it prints the key and value, and in this
case the value is a Pair.
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[Python-Dev] Possible wrong behavior of the dict?
Hello!
In order to explain, let define subclass of dict:
class Pair:
def __init__(self, key, val):
self.key = key
self.val = val
class MyDict(dict):
#
def __init__(self, *args, **kwds):
if len(args) 1:
raise TypeError('Expected at most 1 arguments, but got %d' %
len(args))
for key, val in args[0]:
self[key] = val
for key, val in kwds.items():
self[key] = val
def __getitem__(self, key):
pair = dict.__getitem__(key)
return pair.value
def __setitem__(self, key, val):
if key in self:
pair = dict.__getitem__(key)
pair.value = value
else:
pair = Pair(key, val)
dict.__setitem__(self, key, pair)
def values(self):
for key in self:
p = dict.__getitem__(self, key)
yield p.value
def items(self):
for key, p in dict.__iter__(self):
yield p.key, p.value
The simple test give me strange result:
d = MyDict([('a', 1), ('b', 2), ('c', 3)])
dict(d)
{'a': __main__.Pair at 0x104ca9e48,
'b': __main__.Pair at 0x104ca9e80,
'c': __main__.Pair at 0x104ca9eb8}
instead of {'a':1, 'b':2, 'c':3}.
Is this right behavior of the dict?
---
Zaur Shibzukhov
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Re: [Python-Dev] Possible wrong behavior of the dict?
Yes... But I expected that dict constructor will use `__getitem__` or
`items` method of MyDict instance in order to retrieve items of the MyDict
instance during construction of the dict instance... Instead it interpreted
MyDict instance as the dict instance during construction of new dict.This
exactly caused my confusion.
---
*Zaur Shibzukhov*
2015-03-17 22:12 GMT+03:00 Brett Cannon br...@python.org:
On Tue, Mar 17, 2015 at 3:05 PM Zaur Shibzukhov szp...@gmail.com wrote:
Hello!
In order to explain, let define subclass of dict:
class Pair:
def __init__(self, key, val):
self.key = key
self.val = val
class MyDict(dict):
#
def __init__(self, *args, **kwds):
if len(args) 1:
raise TypeError('Expected at most 1 arguments, but got %d' %
len(args))
for key, val in args[0]:
self[key] = val
for key, val in kwds.items():
self[key] = val
def __getitem__(self, key):
pair = dict.__getitem__(key)
return pair.value
def __setitem__(self, key, val):
if key in self:
pair = dict.__getitem__(key)
pair.value = value
else:
pair = Pair(key, val)
dict.__setitem__(self, key, pair)
def values(self):
for key in self:
p = dict.__getitem__(self, key)
yield p.value
def items(self):
for key, p in dict.__iter__(self):
yield p.key, p.value
The simple test give me strange result:
d = MyDict([('a', 1), ('b', 2), ('c', 3)])
dict(d)
{'a': __main__.Pair at 0x104ca9e48,
'b': __main__.Pair at 0x104ca9e80,
'c': __main__.Pair at 0x104ca9eb8}
instead of {'a':1, 'b':2, 'c':3}.
Is this right behavior of the dict?
Yes because in your __setitem__ call you are storing the value as the
Pair. So when dict prints its repr it prints the key and value, and in this
case the value is a Pair.
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Re: [Python-Dev] Possible wrong behavior of the dict?
* Zaur Shibzukhov szp...@gmail.com [2015-03-17 22:29:07 +0300]: Yes... But I expected that dict constructor will use `__getitem__` or `items` method of MyDict instance in order to retrieve items of the MyDict instance during construction of the dict instance... Instead it interpreted MyDict instance as the dict instance during construction of new dict.This exactly caused my confusion. Subclassing builtins is always a recipe for trouble, because the C implementation doesn't necessarily call your Python methods. You should probably use collections.UserDict or collections.abc.(Mutable)Mapping instead: https://docs.python.org/3/library/collections.html#collections.UserDict https://docs.python.org/3/library/collections.abc.html#collections.abc.Mapping Florian -- http://www.the-compiler.org | m...@the-compiler.org (Mail/XMPP) GPG: 916E B0C8 FD55 A072 | http://the-compiler.org/pubkey.asc I love long mails! | http://email.is-not-s.ms/ pgp57NLMvC4Lp.pgp Description: PGP signature ___ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] Possible wrong behavior of the dict?
Thanks.
---
*Zaur Shibzukhov*
2015-03-17 22:48 GMT+03:00 Brett Cannon br...@python.org:
On Tue, Mar 17, 2015 at 3:46 PM Zaur Shibzukhov szp...@gmail.com wrote:
So in such cases it should not subclassed `dict`, but
`collections.MutableMapping`, for example?
Yes (see the comment at
https://hg.python.org/cpython/file/22a0c925a7c2/Objects/dictobject.c#l2003
).
-Brett
---
*Zaur Shibzukhov*
2015-03-17 22:38 GMT+03:00 Brett Cannon br...@python.org:
On Tue, Mar 17, 2015 at 3:29 PM Zaur Shibzukhov szp...@gmail.com
wrote:
Yes... But I expected that dict constructor will use `__getitem__` or
`items` method of MyDict instance in order to retrieve items of the MyDict
instance during construction of the dict instance... Instead it interpreted
MyDict instance as the dict instance during construction of new dict.This
exactly caused my confusion.
It's because you subclassed dict. Copying is optimized to skip over
using the methods you listed when the object is a dict and so we know the
structure of the object at the C level. You can look at
https://hg.python.org/cpython/file/22a0c925a7c2/Objects/dictobject.c#l1997
to see the actual code.
-Brett
---
*Zaur Shibzukhov*
2015-03-17 22:12 GMT+03:00 Brett Cannon br...@python.org:
On Tue, Mar 17, 2015 at 3:05 PM Zaur Shibzukhov szp...@gmail.com
wrote:
Hello!
In order to explain, let define subclass of dict:
class Pair:
def __init__(self, key, val):
self.key = key
self.val = val
class MyDict(dict):
#
def __init__(self, *args, **kwds):
if len(args) 1:
raise TypeError('Expected at most 1 arguments, but got
%d' % len(args))
for key, val in args[0]:
self[key] = val
for key, val in kwds.items():
self[key] = val
def __getitem__(self, key):
pair = dict.__getitem__(key)
return pair.value
def __setitem__(self, key, val):
if key in self:
pair = dict.__getitem__(key)
pair.value = value
else:
pair = Pair(key, val)
dict.__setitem__(self, key, pair)
def values(self):
for key in self:
p = dict.__getitem__(self, key)
yield p.value
def items(self):
for key, p in dict.__iter__(self):
yield p.key, p.value
The simple test give me strange result:
d = MyDict([('a', 1), ('b', 2), ('c', 3)])
dict(d)
{'a': __main__.Pair at 0x104ca9e48,
'b': __main__.Pair at 0x104ca9e80,
'c': __main__.Pair at 0x104ca9eb8}
instead of {'a':1, 'b':2, 'c':3}.
Is this right behavior of the dict?
Yes because in your __setitem__ call you are storing the value as the
Pair. So when dict prints its repr it prints the key and value, and in
this
case the value is a Pair.
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Re: [Python-Dev] PEP 448 review
On Mon, Mar 16, 2015 at 7:11 PM Neil Girdhar mistersh...@gmail.com wrote: Hi everyone, I was wondering what is left with the PEP 448 ( http://bugs.python.org/issue2292) code review? Big thanks to Benjamin, Ethan, and Serhiy for reviewing some (all?) of the code. What is the next step of this process? My suspicion is that if no one steps up between now and PyCon to do a complete code review of the final patch, we as a group will try to get it done at the PyCon sprints. I have made the issue a release blocker to help make sure it gets reviewed and doesn't accidentally get left behind. ___ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
