I can't instanciate a simple class in Python: newbe question.

Question

Hello all. I want to generate a Python class via a file. This is a very simple file, named testy.py:

def __init__(self,var):
    print (var)

When I try to instantiate it I get:

>>> import testy
>>> testy('1')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'module' object is not callable

Then , I try something else:

class testy_rev1:
    def __init__(self,var):
    print (var)

I try to instanicate it and I get:

>>> import testy_rev1
>>> a=testy_rev1('1')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'module' object is not callable
>>> a=testy_rev1.testy_rev1('1')
1

What I am looking for is a way to import it from a file w/o resorting to:

import <module name>.<module name>

Answer 1

Attempt 1 failed because you were not defining a class, just a function (which you fixed with attempt 2).

Attempt 2 is failing because you looking at the import statement like it is a Java import statement. In Python, an import makes a module object that can be used to access items inside it. If you want use a class with in a module without first specifying the module you want to use the following:

from my_module import MyClass
a = MyClass()

As a side note, your print method in the 2nd attempt in not indented after the __init__ method. This might just me a formatting error when you posted here, but it will not run the code how you expect.

Answer 2

import x imports a module called x. import y.x imports the module d from the module/package y. Anything in this module is refered to as x.stuff or y.x.stuff. That's how it works and they won't change the language for your convenience ;)

You can always do from module import thingy. But consider that importing the whole module is usually preferred over this... for a reason (to make clearer where it came from, to avoid namespace clashes, because "explicit is better than mplicit")!

Answer 3

With a file called testy.py with this:

class testy_rev1:
    def __init__(self, var):
        print (var)

You will have to do either:

>>> import testy
>>> testy.testy_rev1('1')

Or:

>>> from testy import testy_rev1
>>> testy_rev1('1')

Or (not recommended, since you will not see where the definition came from in the source):

>>> from testy import *
>>> testy_rev1('1')

Other than that I do not know how you could do it.