<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def coerceBigInt(x):
 """ Retrieves a BigInt from @x or returns None if @x is not a type that can be converted. """

    # BigInt's are easy.
    if isinstance(x, BigInt):
        return x

    # Convert ints and longs using the constructor
    elif isinstance(x, (long, int)):
        return BigInt(x)

    else:
        return None