Question

I need to have an import in __init__() method (because i need to run that import only when i instance the class).

But i cannot see that import outside __init__(), is the scope limited to__init__? how to do?

Answer 1

Imported names are bound to the current scope, so an import inside a function binds to a local name only.

If you absolutely have to import something in __init__ that then needs to be globally avaliable, mark the imported name as global first:

>>> def foo():
...     global sys
...     import sys
... 
>>> sys
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'sys' is not defined
>>> foo()
>>> sys
<module 'sys' (built-in)>

but this usually leads to strange and wonderfully difficult to locate bugs. Don’t do that, just make your imports at module scope instead.

If you need the imported name within other class methods, you could also assign the imported name to a instance variable:

class Foo(object):
    def __init__(self):
        import os
        self.join = os.path.join

but again, that’s not the best practice to use.