Subsets a dictionary based on a set of specified keys to include

subdict.py

def subdict(d, include_keys=[]):
    """
    Subsets a :dict: by keys specified in :include_keys:
    
    >>> subdict({ 'a': 1, 'b': 2, 'c': 3 }, ['a', 'c'])
    { 'a': 1', 'c': 3 }
    >>> subdict({ 'a': 1, 'b': 2, 'c': 3 }, ['x', 'y'])
    {}
    >>> subdict({}, [])
    {}
    >>> subdict({}, None)
    {}
    >>> subdict(None, [])
    None
    """
    if d is None: return None
    if not include_keys: return {}
    ret = {}
    for key in d.iterkeys():
        if key in include_keys:
            ret[key] = d[key]
    return ret