def merge(a, b):
    """Merge two deep dicts non-destructively

    Uses a stack to avoid maximum recursion depth exceptions

    >>> a = {'a': 1, 'b': {1: 1, 2: 2}, 'd': 6}
    >>> b = {'c': 3, 'b': {2: 7}, 'd': {'z': [1, 2, 3]}}
    >>> c = merge(a, b)
    >>> from pprint import pprint; pprint(c)
    {'a': 1, 'b': {1: 1, 2: 7}, 'c': 3, 'd': {'z': [1, 2, 3]}}
    """
    assert quacks_like_dict(a), quacks_like_dict(b)
    dst = a.copy()

    stack = [(dst, b)]
    while stack:
        current_dst, current_src = stack.pop()
        for key in current_src:
            if key not in current_dst:
                current_dst[key] = current_src[key]
            else:
                if (quacks_like_dict(current_src[key]) and
                        quacks_like_dict(current_dst[key])):
                    stack.append((current_dst[key], current_src[key]))
                elif (quacks_like_list(current_src[key]) and
                        quacks_like_list(current_dst[key])):
                    current_dst[key].extend(current_src[key])
                else:
                    current_dst[key] = current_src[key]
    return dst
def merge ( a , b ) : assert quacks_like_dict ( a ) , quacks_like_dict ( b ) dst = a . copy ( ) stack = [ ( dst , b ) ] while stack : current_dst , current_src = stack . pop ( ) for key in current_src : if key not in current_dst : current_dst [ key ] = current_src [ key ] else : if ( quacks_like_dict ( current_src [ key ] ) and quacks_like_dict ( current_dst [ key ] ) ) : stack . append ( ( current_dst [ key ] , current_src [ key ] ) ) elif ( quacks_like_list ( current_src [ key ] ) and quacks_like_list ( current_dst [ key ] ) ) : current_dst [ key ] . extend ( current_src [ key ] ) else : current_dst [ key ] = current_src [ key ] return dst
Merge two deep dicts non-destructively

    Uses a stack to avoid maximum recursion depth exceptions

    >>> a = {'a': 1, 'b': {1: 1, 2: 2}, 'd': 6}
    >>> b = {'c': 3, 'b': {2: 7}, 'd': {'z': [1, 2, 3]}}
    >>> c = merge(a, b)
    >>> from pprint import pprint; pprint(c)
    {'a': 1, 'b': {1: 1, 2: 7}, 'c': 3, 'd': {'z': [1, 2, 3]}}