code: def cert_verify(self, conn, url, verify, cert):
          
          if url.lower().startswith('https') and verify:
  
              cert_loc = None
  
              # Allow self-specified cert location.
              if verify is not True:
                  cert_loc = verify
  
              if not cert_loc:
                  cert_loc = DEFAULT_CA_BUNDLE_PATH
  
              if not cert_loc or not os.path.exists(cert_loc):
                  raise IOError("Could not find a suitable TLS CA certificate bundle, "
                                "invalid path: {0}".format(cert_loc))
  
              conn.cert_reqs = 'CERT_REQUIRED'
  
              if not os.path.isdir(cert_loc):
                  conn.ca_certs = cert_loc
              else:
                  conn.ca_cert_dir = cert_loc
          else:
              conn.cert_reqs = 'CERT_NONE'
              conn.ca_certs = None
              conn.ca_cert_dir = None
  
          if cert:
              if not isinstance(cert, basestring):
                  conn.cert_file = cert[0]
                  conn.key_file = cert[1]
              else:
                  conn.cert_file = cert
                  conn.key_file = None
              if conn.cert_file and not os.path.exists(conn.cert_file):
                  raise IOError("Could not find the TLS certificate file, "
                                "invalid path: {0}".format(conn.cert_file))
              if conn.key_file and not os.path.exists(conn.key_file):
                  raise IOError("Could not find the TLS key file, "
                                "invalid path: {0}".format(conn.key_file))
docs: Verify a SSL certificate. This method should not be called from user
          code, and is only exposed for use when subclassing the
          :class:`HTTPAdapter <requests.adapters.HTTPAdapter>`.
  
          :param conn: The urllib3 connection object associated with the cert.
          :param url: The requested URL.
          :param verify: Either a boolean, in which case it controls whether we verify
              the server's TLS certificate, or a string, in which case it must be a path
              to a CA bundle to use
          :param cert: The SSL certificate to verify.