<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _findroot(self, x):
 """Internal MIBDict function used to find a partial OID"""

        if x.startswith("."):
            x = x[1:]
        if not x.endswith("."):
            x += "."
        max = 0
        root = "."
        root_key = ""
        for k in six.iterkeys(self):
            if x.startswith(k + "."):
                if max < len(k):
                    max = len(k)
                    root = self[k]
                    root_key = k
        return root, root_key, x[max:-1]