Does Python import statement also import dependencies automatically?

Question

I have the following file app.py

class Baz():
    def __init__(self, num):
        self.a = num
        print self.a

def foo(num):
    obj = Ba         


        

Answer 1

As @DavidZ already mentioned the whole Python file gets compiled when we import it. But another special thing happens when a function body is parsed, a function knows which variables it should look for in local scope and which variables it should look for in global scope(well there are free variables too).

>>> import dis
>>> dis.dis(foo)
  7           0 LOAD_GLOBAL              0 (Baz)
              3 LOAD_FAST                0 (num)
              6 CALL_FUNCTION            1
              9 STORE_FAST               1 (obj)
             12 LOAD_CONST               0 (None)
             15 RETURN_VALUE

So, here Baz must be fetched from global scope.

But how to identify this global scope when we import app.py in another file?

Well, each function has a special attribute __globals__ attached to it which contains its actual global namespace. Hence, that's the source of Baz:

>>> foo.__globals__['Baz']

So, app's module dictionary and foo.__globals__ point to the same object:

>>>sys.modules['app'].__dict__ is foo.__globals__ 
True

Due to this even if you define another variable named Baz in main.py after importing foo it will still access the actual Baz.

From data-model page:

__globals__ func_globals:

A reference to the dictionary that holds the function’s global variables — the global namespace of the module in which the function was defined.