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Version 0.14.1 "Retrofuturistic edition"

**Language version**:

- Support Python 3.6. First released in 2016, supported until 2021, most distros should have it by now.
- This will be the final release that supports Python 3.4; upstream support for 3.4 ended in March 2019.

**New**:

- ``Popper``, a pop-while iterator.
- ``window``, a length-n sliding window iterator for general iterables.
- ``autoref[]`` can now be nested.
- ``dbg[]`` now supports also an expression variant, customizable by lexically assigning ``dbgprint_expr``. See the README on macros for details.

**Bugfixes**:

- Fix crash when SymPy or mpmath are not installed.
- ``mogrify`` is now part of the public API, as it should have been all along.
- Docs: Mention the ``mg`` function in the README.

**Non-breaking changes**:

- Future-proof ``namelambda`` for Python 3.8.
- Docs: ``dbg[]`` is now listed as a convenience feature in the README.

**Bugfixes**:

 - ``setup.py``: macros are not zip safe, because ``ZipImporter`` fails to return source code for the module and MacroPy needs that.
 - fix splicing in the ``do[]`` macro; ``ExpandedDoView`` should now work correctly
 - fix lambda handling in the ``lazify`` macro
 - fix ``dict_items`` handling in ``mogrify`` (fixes the use of the ``curry`` macro with code using ``frozendict``)

**New**:

 - ``roview``: a read-only view into a sequence. Behaves mostly the same as ``view``, but has no ``__setitem__`` or ``reverse``.
 - ``mg``: a decorator to mathify a gfunc, so that it will ``m()`` the generator instances it makes.
 - The ``do[]`` macro now supports ``delete[name]`` to delete a local variable previously created in the same do-expression using ``local[name << value]``.
 - ``envify`` block macro, to make formal parameters live in an unpythonic ``env``.
 - ``autoref`` block macro, to implicitly reference attributes of an object (for reading only).

**Breaking changes**:

 - The ``macropy3`` bootstrapper now takes the ``-m`` option; ``macropy3 -m somemod``, like ``python3 -m somemod``. The alternative is to specify a filename positionally; ``macropy3 somescript.py``, like ``python3 somescript.py``. In either case, the bootstrapper will import the module in a special mode that pretends its ``__name__ == '__main__'``, to allow using the pythonic conditional main idiom also in macro-enabled code.
 - The constructor of the writable ``view`` now checks that the input is not read-only (``roview``, or a ``Sequence`` that is not also a ``MutableSequence``) before allowing creation of the writable view.
 - ``env`` now checks finalization status also when deleting attrs (a finalized ``env`` cannot add or delete bindings)

**Non-breaking improvements**:

 - ``env`` now provides also the ``collections.abc.MutableMapping`` API.
 - The ``tco`` macro now skips nested ``continuations`` blocks (to allow [Lispython](https://github.com/Technologicat/pydialect/tree/master/lispython) in [Pydialect](https://github.com/Technologicat/pydialect) to support ``continuations``).
 - ``setup.py`` now installs the ``macropy3`` bootstrapper.