'Return field position by its ASN.1 type.
Parameters
tagSet: :class:`~pysnmp.type.tag.TagSet`
ASN.1 tag set distinguishing one ASN.1 type from others.
Returns
: :py:class:`int`
ASN.1 type position in fields set
Raises
: :class:`~pyasn1.error.PyAsn1Error`
If *tagSet* is not present or ASN.1 types are not unique within callee *NamedTypes*'

def getPositionByType(self, tagSet):

    try:
        return self.__tagToPosMap[tagSet]
    except KeyError:
        raise error.PyAsn1Error(('Type    %s    not    found' % (tagSet,)))
