Iterator pipe in Python

iterpipe.py

"""Iterator Utility that use iterator with method chains.
"""
#
# Copyright (c) 2012 Satoshi Fukutomi <info@fuktommy.com>.
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
# 1. Redistributions of source code must retain the above copyright
#    notice, this list of conditions and the following disclaimer.
# 2. Redistributions in binary form must reproduce the above copyright
#    notice, this list of conditions and the following disclaimer in the
#    documentation and/or other materials provided with the distribution.
#
# THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
# ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
# OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
# HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
# OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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__all__ = ['wrap', 'Command']


class Pipe(object):
    """Iterator pipe wrapper.
    """

    def __init__(self, iterable, command = None):
        """Create new pipe with iterable object.
        """
        self._inner = iterable
        self._command = command

    def __iter__(self):
        for i in self._inner:
            if self._command is None:
                yield i
            else:
                for j in self._command.execute(i):
                    yield j
        if self._command is not None:
            for j in self._command.finalize():
                yield j

    def list(self):
        """Convert as list.

        >>> wrap([1, 2, 3]).list()
        [1, 2, 3]
        """
        return list(self)

    def pipe(self, command):
        """Create new instance with pipe command.

        wrap([1, 2, 3]).filter(lambda e: (e, e * 2)).list()
        [1, 2, 2, 4, 3, 6]
        """
        if isinstance(command, Command):
            return Pipe(self, command)
        if callable(command):
            return Pipe(self, CallbackCommand(command))
        raise TypeError('invalid command')

    def filter(self, callback):
        """Filter. Elements callback returns true are survive.

        >>> wrap([1, 2, 3]).filter(lambda e: e % 2 == 1).list()
        [1, 3]
        """
        command = lambda e: (e,) if callback(e) else ()
        return Pipe(self, CallbackCommand(command))

    def map(self, callback):
        """Map callback all elements.

        >>> wrap([1, 2, 3]).map(lambda e: e * 2).list()
        [2, 4, 6]
        """
        command = lambda e: (callback(e),)
        return Pipe(self, CallbackCommand(command))


def wrap(iterable):
    """Create new iterator pipe.

    >>> (wrap([1, 2, 3, 4, 5]).filter(lambda e: e % 2 == 1)
    ...  .map(lambda e: e * 2).list())
    [2, 6, 10]
    """
    return Pipe(iterable)


class Command(object):
    """Pipe command interface.

    >>> class Counter(Command):
    ...     def __init__(self): self._count = 0
    ...     def execute(self, element): self._count += 1; return ()
    ...     def finalize(self): return (self._count,)
    >>> wrap([2, 4, 6]).pipe(Counter()).list()
    [3]
    """
    def execute(self, element):
        """Execute an element, return iteratable.
        """
        return (element,)

    def finalize(self):
        """Finalize loop, return iteratable.
        """
        return ()


class CallbackCommand(Command):
    def __init__(self, callback):
        self._callback = callback

    def execute(self, element):
        return self._callback(element)


def _test():
    import doctest
    doctest.testmod()

if __name__ == '__main__':
    _test()