At what stage or level does the default operation occur?

In Python, the default operation (for example, calling a method or evaluating an expression) is performed at the interpreter level during program execution.

That is, when the interpreter encounters a function call or operation, it immediately executes it unless lazy evaluation is used (for example, generators or lazy iterators).

Example:

result = 5 + 3  # the addition operation is performed immediately during execution

Thus, execution occurs at runtime when the interpreter reads and executes the code.