Allow tuple unpacking on classes defined with @attr.s

unpackable.py

# Allow tuple unpacking on classes defined with
# @attr.s decorator. Uses the attribute information
# from the definition of the class using attrs
#
# See also:
#    http://www.attrs.org
#    https://github.com/python-attrs/attrs
import hashlib
import linecache


from toolz import curry


__author__ = 'egregius313'


@curry
def unpackable(cls, attrs=None):
    """
    Take a class defined using the @attr.s method
    and define a __iter__ method to allow for easier
    pattern matching variable definitions.

    Unpacking order is the same as the order @attr.s
    uses for methods like __init__

    The `attrs' argument must be either iterable or None.
    If the argument is iterable, only attributes with those names
    will be used. Otherwise, all attributes defined with attr.ib()
    will be unpacked.

    >>> @unpackable
    ... @attr.s
    ... class Person:
    ...     name = attr.ib()
    ...     age = attr.ib()
    ...
    >>> people = [
    ...     Person('Jonathan', 35),
    ...     Person('Rick', 26),
    ...     Person('Samuel', 20),
    ...     Person('Brian', 39),
    ... ]
    ...
    >>> for name, age in people:
    ...     print(name, 'is', age, 'years old.')
    ...
    Jonathan is 35 years old
    Rick is 26 years old
    Samuel is 20 years old
    Brian is 39 years old
    """
    if hasattr(cls, '__iter__'):
        return cls

    if attrs is None:
        attributes = tuple(a.name for a in cls.__attrs_attrs__)
    else:
        attributes = tuple(
            a.name for a in cls.__attrs_attrs__
            if a.name not in attrs
        )

    print(attributes)

    lines = [
        'def __iter__(self):',
    ]

    if attributes:
        for attrib in attributes:
            lines.append('    yield self.%s' % attrib)
    else:
        lines.append('    yield from ()')

    sha1 = hashlib.sha1()
    sha1.update(repr(attributes).encode('utf-8'))
    unique_filename = '<unpackable generated iter %s>' % (sha1.hexdigest(),)

    # The additional newline helps inspect.getsource
    script = '\n'.join(lines) + '\n'
    globs = {}
    locs = {}
    bytecode = compile(script, unique_filename, "exec")
    eval(bytecode, globs, locs)

    linecache.cache[unique_filename] = (
        len(script),
        None,
        script.splitlines(True),
        unique_filename,
    )

    cls.__iter__ = locs['__iter__']

    return cls