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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_evidence(assay):
 """Given an activity, return an INDRA Evidence object. Parameters assay : dict an activity from the activities list returned by a query to the API Returns ------- ev : :py:class:`Evidence` an :py:class:`Evidence` object containing the kinetics of the """

    kin = get_kinetics(assay)
    source_id = assay.get('assay_chembl_id')
    if not kin:
        return None
    annotations = {'kinetics': kin}
    chembl_doc_id = str(assay.get('document_chembl_id'))
    pmid = get_pmid(chembl_doc_id)
    ev = Evidence(source_api='chembl', pmid=pmid, source_id=source_id,
                  annotations=annotations)
    return ev