There has been some discussion on python-dev about improving interpreter startup time.  Christian Heimes brought up how the os module imports collections (so _Environ can inherit from it) [1], and mentioned a couple of solutions [2].

[1]https://mail.python.org/pipermail/python-dev/2013-October/129312.html
[2]https://mail.python.org/pipermail/python-dev/2013-October/129367.html

Here is a patch for an alternate approach.  It does not require re-implementing MutableMapping (could get out of sync) and does not require rearranging collections.abc.  Instead it uses a metaclass to resolve the import issue lazily.

Nice trick :)

And when the lazy base class gets resolved, the metaclass gets to say "You didn't see anything and I was never here." :)

-1 on such hacks. I much prefer the _abcoll approach.

The collections module is loaded by the io module. You removed "from collections.abc import MutableMapping" from os.py. To be useful, you have also to rewrite the whole io module to remove all references to the collections.abc module, right?

The io module no longer imports collections.abc through the locale module.

Eric, I'm with Antoine. Your patch is too much of a clever hack and uses tricks that are dark magic. _abcoll is much simpler and easier to understand. Plus it can be used from other modules, too.

Not a problem.  It is most definitely a hack. :)  I put in up as an alternative to rearranging the collections module, but agree that doing so is preferable.  I image that Raymond will make a decision on that one.

Christian, go ahead an rearrange the collections module.

Move Lib/collections/abc.py to Lib/_collections_abc.py.

Also, be sure to update source link on line 18 of Doc/library.collections.abc.rst

New changeset 0b6052f2a8ee by Christian Heimes in branch 'default':
Issue #19218: Rename collections.abc to _collections_abc in order to speed up interpreter start
http://hg.python.org/cpython/rev/0b6052f2a8ee

New changeset 7ea831581af4 by Christian Heimes in branch 'default':
Issue #19218: Add facade collections.abc
http://hg.python.org/cpython/rev/7ea831581af4

New changeset 62b6ecd1e463 by Christian Heimes in branch 'default':
Issue #19218: set __name__ of _collections_abc to collections.abc in order to fix tests and keep beautiful qualified names.
http://hg.python.org/cpython/rev/62b6ecd1e463

Thank you very much for your input and assistance!

tip compared to v3.4.0a3:

### normal_startup ###
Min: 0.506533 -> 0.313627: 1.62x faster
Avg: 0.582504 -> 0.441796: 1.32x faster
Significant (t=19.98)
Stddev: 0.02397 -> 0.04366: 1.8213x larger

Thanks, Christian.

For backward compatibility, shouldn't

  import _collections_abc

in the __init__ file be

  import _collections_abc as abc

?

Opened issue 20784 to address the above.