How to flash message with variables in Flask

a = 3
message = "message {} message continues".format(a)  # Using the format method
message = f"message {a} message continues"  # Using f-strings (Python >= 3.6)
message = "message %d message continues" % (a)  # % Formatting
message = "message " + str(a) + " message continues"  # Concatenation
flash(message)