Patsy

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* Fix some deprecation warnings associated with importing from the `collections`
module (rather than `collections.abc`) in Python 3.7+.

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* The Python 3.6.7 and 3.7.1 point releases changed the standard
tokenizer module in a way that broke patsy. Updated patsy to work
with these point releases. (See `131
<https://github.com/pydata/patsy/pull/131>`__ for details.)

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* Dropped support for Python 2.6 and 3.3.
* Update to keep up with ``pandas`` API changes
* More consistent handling of degenerate linear constraints in
:meth:`DesignInfo.linear_constraint` (`89
<https://github.com/pydata/patsy/issues/89>`__)
* Fix a crash in ``DesignMatrix.__repr__`` when ``shape[0] == 0``

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New features:

* On Python 2, accept ``unicode`` strings containing only ASCII
characters as valid formula descriptions in
the high-level formula API (:func:`dmatrix` and friends). This is
intended as a convenience for people using Python 2 with ``from
__future__ import unicode_literals``. (See :ref:`py2-versus-py3`.)

Bug fixes:

* Accept ``long`` as a valid integer type in the new
:class:`DesignInfo` classes. In particular this fixes errors that
arise on 64-bit Windows builds (where ``ndarray.shape`` contains
``long`` objects), like ``ValueError: For numerical factors,
num_columns must be an int.``

* Fix deprecation warnings encountered with numpy 1.10

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Incompatible changes:

* :class:`EvalFactor` and :meth:`ModelDesc.from_formula` no longer
take an ``eval_env`` argument.

* The :func:`design_matrix_builders` function and the
:meth:`factor_protocol.memorize_passes_needed` method now require an
``eval_env`` as an additional argument.

* The :class:`DesignInfo` constructor's arguments have totally
changed. In addition to the changes needed to support the new
features below, we no longer support "shim" DesignInfo objects that
have non-trivial term specifications. This was only included in the
first place to provide a compatibility hook for competing formula
libraries; four years later, no such libraries have shown up. If one
does, we can re-add it, but I'm not going to bother maintaining it
in the mean time...

* Dropped support for Python 3.2.

Other changes:

* Patsy now supports Pandas's new (version 0.15 or later) categorical
objects.

* Formulas (or more precisely, :class:`EvalFactor` objects) now only
keep a reference to the variables required from their environment
instead of the whole environment where the formula was
defined. (Thanks to Christian Hudon.)

* :class:`DesignInfo` has new attributes
:attr:`DesignInfo.factor_infos` and :attr:`DesignInfo.term_codings`
which provide detailed metadata about how each factor and term is
encoded.

* As a result of the above changes, the split between
:class:`DesignInfo` and :class:`DesignMatrixBuilder` is no longer
necessary; :class:`DesignMatrixBuiler` has been eliminated. So for
example, :func:`design_matrix_builders` now returns a list of
:class:`DesignInfo` objects, and you can now pass
:class:`DesignInfo` objects directly to any function for building
design matrices. For compatibility, :class:`DesignInfo` continues to
provide ``.builder`` and ``.design_info`` attributes, so that old
code should continue to work; however, these attributes are
deprecated.

* Ensured that attempting to pickle most Patsy objects raises an
error. This has never been supported, and the interesting cases
failed in any case, but now we're taking a more systematic
approach. (Soon we will add real, supported pickling support.)

* Fixed a bug when running under ``python -OO``.

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* New stateful transforms for computing natural and cylic cubic
splines with constraints, and tensor spline bases with
constraints. (Thanks to `broessli <https://github.com/broessli>`_
and GDF Suez for contributing this code.)

* Dropped support for Python 2.5 and earlier.

* Switched to using a single source tree for both Python 2 and Python
3.

* Added a fast-path to skip NA detection for inputs with boolean
dtypes (thanks to Matt Davis for patch).

* Incompatible change: Sometimes when building a design matrix for a
formula that does not depend on the data in any way, like ``"1 ~
1"``, we have no way to determine how many rows the resulting matrix
should have. In previous versions of patsy, when this occurred we
simply returned a matrix with 1 row. In 0.3.0+, we instead refuse to
guess, and raise an error.

Note that because of the next change listed, this situation occurs
less frequently in 0.3.0 than in previous versions.

* If the ``data`` argument to :func:`build_design_matrices` (or
derived functions like :func:`dmatrix`, :func:`dmatrices`) is a
:class:`pandas.DataFrame`, then we now check its number of rows and
index, and insist that the output design matrices match. This also
means that if ``data`` is a DataFrame, then the error described in
the first bullet above cannot occur -- we will simply return a
column of 1s that is the same size as the input dataframe.

* Worked around some more limitations in py2exe/py2app and friends.