The instance of class
RemoteHeavyDB connects to the HeavyDB instance, and the object it returns can be used to register functions. Then, you define a normal Python function
fahrenheit2celsius. The function is decorated using the instance
heavy of the class
RemoteHeavyDB, and it is provided with the function signature
'double(double)'. With this modification, the decorated function expects a single argument that is a double-precision floating-point value and also returns a double-precision floating-point value. The syntax is similar to function annotations in C/C++.