':param bindings:
list [(``VariableExpression``, ``AtomicExpression``)] to initialize the dictionary
dict {``VariableExpression``: ``AtomicExpression``} to initialize the dictionary'

def __init__(self, bindings=None):

    self.d = {}
    if isinstance(bindings, dict):
        bindings = bindings.items()
    if bindings:
        for (v, b) in bindings:
            self[v] = b
