The types module has an entry for DictProxy.  I am 
unable to find any documentation.

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DictProxy is an implementation detail, perhaps it should
have been left out of types.  I notice there is no CellType
in there.

(you can obtain this type like so:)

>>> type((lambda x: lambda: x)(1).func_closure[0])
<type 'cell'>

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I suggest that it would be better to indicate the purpose
and usage of both CellType in the Library Reference.  If one
is to keep it under the pillow, it should be complete and
uptodate.

Colin W.

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Currently the library reference contains minimal information
on internal objects; here's the entire text of the relevant
section:

"""
2.3.10.10 Internal Objects

See the Python Reference Manual for this information. It
describes stack frame objects, traceback objects, and slice
objects. 
"""

Perhaps cell and dictproxy types should be added to the
language reference manual.  On the other hand, it isn't
clear to me that absolute completeness is desirable.  Any
language or application has some undocumented features; the
fact that they 
are not documented is a signal to the user that their use is
not supported and they may go away without warning in future
versions.

Currently in trunk the types implementation only defines:

DictProxyType = type(TypeType.__dict__)

This is also documented in library/types.rst as:

types.DictProxyType
    The type of dict proxies, such as TypeType.__dict__.

It's the only definition that I could find that comes close to DictProxy.
Does this address the issue?

In 3.x, DictProxy and other internal types are gone from types.