Map.py

from itertools import imap
import json

class Map(object):
    def __init__(self, iterable, steps=[]):
        """
        Construct an iterator that looks up items in the given iterable by index, key, field name, or calls
            a function on them.

        :param iterable: An iterable of "objects"
        """
        self.iterable = iterable
        self.steps = steps

    def from_existing(self, new_step):
        steps = list(self.steps) + [new_step]
        return Map(self.iterable, steps)

    def __getattr__(self, name):
        return self.from_existing(lambda i: getattr(i, name))

    def __getitem__(self, key):
        return self.from_existing(lambda i: i[key])

    def get(self, key, default=None):
        return self.from_existing(lambda i: self._get_even_from_list(i, key, default))

    def __or__(self, func):
        return self.from_existing(func)

    def __call__(self):
        return list(self.__iter__())

    @staticmethod
    def _get_even_from_list(obj, key, default=None):
        if isinstance(obj, dict):
            return obj.get(key, default)
        try:
            return obj[key]
        except IndexError:
            return default

    def __repr__(self):
        return "<MapGet({}) steps={}>".format(self.iterable, self.steps)

    def __iter__(self):
        return imap(
            reduce(
                lambda f, g: lambda x: g(f(x)),  # function composition
                self.steps,
                lambda x: x  # initializer
            ),
            self.iterable
        )

if __name__ == '__main__':
    obj = [{"x":[{"y":{"z":5}}]}, {"x":[{"y":{"z":6}}]}]
    m1 = Map(obj)["x"][0]["y"]
    m2 = Map(m1)
    print((m1 | json.dumps)())
    print((m2['z'] | (lambda x: x**2))())
    # ['{"z": 5}', '{"z": 6}']
    # [25, 36]