How to use the xmlsec.cryptoAppKeyLoad function in xmlsec

# Create and initialize keys manager, we use a simple list based
    # keys manager, implement your own KeysStore klass if you need
    # something more sophisticated
    mngr = xmlsec.KeysMngr()
    if mngr is None:
        print "Error: failed to create keys manager."
        return None
    if xmlsec.cryptoAppDefaultKeysMngrInit(mngr) < 0:
        print "Error: failed to initialize keys manager."
        mngr.destroy()
        return None
    # Load private RSA key
    if not check_filename(key_file):
        mngr.destroy()
        return None
    key = xmlsec.cryptoAppKeyLoad(key_file, xmlsec.KeyDataFormatPem,
                                  None, None, None);
    if key is None:
        print "Error: failed to load rsa key from file \"%s\"" % key_file
        mngr.destroy()
        return None
    # Set key name to the file name, this is just an example!
    if key.setName(key_file) < 0:
        print "Error: failed to set key name for key from \"%s\"" % key_file
        key.destroy()
        mngr.destroy()
        return None
    # Add key to keys manager, from now on keys manager is responsible
    # for destroying key
    if xmlsec.cryptoAppDefaultKeysMngrAdoptKey(mngr, key) < 0:
        print "Error: failed to add key from \"%s\" to keys manager" % file
        key.destroy()

if xmlsec.cryptoAppInit(None) < 0:
        raise SignatureError('crypto initialization failed')
      if xmlsec.cryptoInit() < 0:
        raise SignatureError('xmlsec-crypto initialization failed')

      # load the input
      doc = libxml2.parseDoc(xml)
      if not doc or not doc.getRootElement():
        raise SignatureError('error parsing input xml')
      node = xmlsec.findNode(doc.getRootElement(), xmlsec.NodeSignature,
                             xmlsec.DSigNs)
      if not node:
        raise SignatureError("couldn't find root node")

      # load the private key
      key = xmlsec.cryptoAppKeyLoad(self.key_file, xmlsec.KeyDataFormatPem,
                                    self.key_pwd, None, None)
      if not key:
        raise SignatureError('failed to load the private key %s' % self.key_file)

      if xmlsec.cryptoAppKeyCertLoad(key, self.cert_file, xmlsec.KeyDataFormatPem) < 0:
        print "Error: failed to load pem certificate \"%s\"" % self.cert_file
        return self.cleanup(doc, dsigctx)

      keymngr = xmlsec.KeysMngr()
      xmlsec.cryptoAppDefaultKeysMngrInit(keymngr)
      xmlsec.cryptoAppDefaultKeysMngrAdoptKey(keymngr, key)
      dsigctx = xmlsec.DSigCtx(keymngr)

      if key.setName(self.key_file) < 0:
        raise SignatureError('failed to set key name')

if doc is None or doc.getRootElement() is None:
	print "Error: unable to parse file \"%s\"" % tmpl_file
        return cleanup(doc)

    # Find start node
    node = xmlsec.findNode(doc.getRootElement(),
                           xmlsec.NodeSignature, xmlsec.DSigNs)

    # Create signature context, we don't need keys manager in this example
    dsig_ctx = xmlsec.DSigCtx()
    if dsig_ctx is None:
        print "Error: failed to create signature context"
        return cleanup(doc)

    # Load private key, assuming that there is not password
    key = xmlsec.cryptoAppKeyLoad(key_file, xmlsec.KeyDataFormatPem,
                                  None, None, None)
    if key is None:
        print "Error: failed to load private pem key from \"%s\"" % key_file
        return cleanup(doc, dsig_ctx)
    dsig_ctx.signKey = key

    # Set key name to the file name, this is just an example!
    if not check_filename(key_file):
        return cleanup(doc, dsig_ctx)
    if key.setName(key_file) < 0:
        print "Error: failed to set key name for key from \"%s\"" % key_file
        return cleanup(doc, dsig_ctx)

    # Verify signature
    if dsig_ctx.verify(node) < 0:
        print "Error: signature verify"

print "Error: failed to add key info"
        return cleanup(doc)
    
    keyNameInfo = keyInfoNode.addKeyName(None)
    if keyNameInfo is None:
        print "Error: failed to add key name"
        return cleanup(doc)

    # Create signature context, we don't need keys manager in this example
    dsig_ctx = xmlsec.DSigCtx()
    if dsig_ctx is None:
        print "Error: failed to create signature context"
        return cleanup(doc)

    # Load private key, assuming that there is not password
    key = xmlsec.cryptoAppKeyLoad(key_file, xmlsec.KeyDataFormatPem,
                                  None, None, None)
    if key is None:
        print "Error: failed to load private pem key from \"%s\"" % key_file
        return cleanup(doc, dsig_ctx)
    dsig_ctx.signKey = key

    # Set key name to the file name, this is just an example!
    if key.setName(key_file) < 0:
        print "Error: failed to set key name for key from \"%s\"" % key_file
        return cleanup(doc, dsig_ctx)

    # Sign the template
    if dsig_ctx.sign(signNode) < 0:
        print "Error: signature failed"
        return cleanup(doc, dsig_ctx)

# Find start node
    node = xmlsec.findNode(doc.getRootElement(), xmlsec.NodeSignature,
                           xmlsec.DSigNs)
    if node is None:
	print "Error: start node not found in \"%s\"" % tmpl_file
        return cleanup(doc)
        
    # Create signature context, we don't need keys manager in this example
    dsig_ctx = xmlsec.DSigCtx()
    if dsig_ctx is None:
        print "Error: failed to create signature context"
        return cleanup(doc)

    # Load private key, assuming that there is not password
    key = xmlsec.cryptoAppKeyLoad(key_file, xmlsec.KeyDataFormatPem,
                                  None, None, None)
    if key is None:
        print "Error: failed to load private pem key from \"%s\"" % key_file
        return cleanup(doc, dsig_ctx)
    dsig_ctx.signKey = key

    # Set key name to the file name, this is just an example!
    if key.setName(key_file) < 0:
        print "Error: failed to set key name for key from \"%s\"" % key_file
        return cleanup(doc, dsig_ctx)

    # Sign the template
    if dsig_ctx.sign(node) < 0:
        print "Error: signature failed"
        return cleanup(doc, dsig_ctx)

return cleanup(doc)
    
    if keyInfoNode.addX509Data() is None:
        print "Error: failed to add X509Data node"
        return cleanup(doc)

    # Create signature context, we don't need keys manager in this example
    dsig_ctx = xmlsec.DSigCtx()
    if dsig_ctx is None:
        print "Error: failed to create signature context"
        return cleanup(doc)

    # Load private key, assuming that there is not password
    if not check_filename(key_file):
        return cleanup(doc, dsig_ctx)
    key = xmlsec.cryptoAppKeyLoad(key_file, xmlsec.KeyDataFormatPem,
                                  None, None, None)
    if key is None:
        print "Error: failed to load private pem key from \"%s\"" % key_file
        return cleanup(doc, dsig_ctx)
    dsig_ctx.signKey = key

    # Load certificate and add to the key
    if not check_filename(cert_file):
        return cleanup(doc, dsig_ctx)
    if xmlsec.cryptoAppKeyCertLoad(key, cert_file, xmlsec.KeyDataFormatPem) < 0:
        print "Error: failed to load pem certificate \"%s\"" % cert_file
        return cleanup(doc, dsig_ctx)

    # Set key name to the file name, this is just an example!
    if key.setName(key_file) < 0:
        print "Error: failed to set key name for key from \"%s\"" % key_file