Python deferred execution helper.

defer.py

from collections import deque
from functools import partial, wraps


class Deferred:
    """
    Deferred functions execution.

    Usage:

        >>> with Deferred() as deferred:
        ...     for x in range(3):
        ...        deferred.call(lambda x: x*2, x)
        ...     results = list(deferred.results())
        >>> results
        [0, 2, 4]
        >>> a = []
        >>> with Deferred() as deferred:
        ...    deferred.call(a.append, 1)
        ...    deferred.run_all()
        ...    assert a == [1]
        ...    @deferred
        ...    def append(x):
        ...        a.append(x)
        ...    append(2)
        ...    assert a == [1]
        >>> a
        [1, 2]

    """

    def __init__(self):
        self._deferred = deque()

    def __enter__(self):
        return self

    def __call__(self, fn):
        @wraps(fn)
        def wrapper(*args, **kwargs):
            self.call(fn, *args, **kwargs)
        return wrapper

    def call(self, fn, *args, **kwargs):
        self._deferred.append(partial(fn, *args, **kwargs))

    def __exit__(self, exc_type, exc_val, exc_tb):
        self.run_all()

    def results(self):
        while self._deferred:
            yield self._deferred[0]()
            self._deferred.popleft()

    def run_all(self):
        for _ in self.results():
            pass