How are import statements in plpython handled?

Question

I have a plypython function which does some json magic. For this it obviously imports the json library.

Is the import called on every call to the function? Are there

Answer 1

The declaration in the body of a PL/Python function will eventually become an ordinary Python function and will thus behave as such. When a Python function imports a module for the first time the module is cached in the sys.modules dictionary (https://docs.python.org/3/reference/import.html#the-module-cache). Subsequent imports of the same module will simply bind the import name to the module object found in the dictionary. In a sense, what I'm saying may cast some doubt on the usefulness of the tip given in the accepted answer, since it makes it somewhat redundant, as Python already does a similar caching for you.

To sum things up, I'd say that if you import in the standard way of simply using the import or from [...] import constructs, then you need not worry about repeated imports, in functions or otherwise, Python has got you covered.

On the other hand, Python allows you to bypass its native import semantics and to implement your own (with the __import__() function and importlib module). If this is what you're doing, maybe you should review what's available in the toolbox (https://docs.python.org/3/reference/import.html).