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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_unit(a):
 """Extract the time unit from array's dtype"""

    typestr = a.dtype.str
    i = typestr.find('[')
    if i == -1:
        raise TypeError("Expected a datetime64 array, not %s", a.dtype)
    return typestr[i + 1: -1]