在Python中将一个类导入另一个类

Question

as I'm still learning python I came up to a problem.

Why does this work:

class SomeOtherClass(object):
    def __init__(self):
        self.number = 10
        print(self.number)

    def increase(self):
        self.number += 1
        print(self.number)

class MyMainClass(object):
    def __init__(self):
        self.otherClass = MyClass()

app = MyMainClass() #Output: 10
app.otherclass.increase() #Output: 11

but this doesn't:

from tkinter import *

class MyMainClass(object):
    def __init__(self):
        self.tk = Tkinter() # <-- Error: see below.

app = MyMainClass()
app.tk.title("My window")
...

Both times I include a class, but in the second example it says:

NameError: global name 'Tkinter' is not defined

Where's the difference between those examples and how can I solve this, so I'm able to use tkinter in my class?

Thanks for your help.

Answer 1

Perhaps you meant Tk() ? the tkinter module on Python 3.x does not seem to contain a class Tkinter .

As to the meaning of your question and example... well, the examples are absolutely irrelevant, and the question should simply be "why can't I create an instance of Tkinter " or something.

Python Lesson: This is also a good example of why it's a bad idea to use star imports (ie from <module> import * , because * looks like a star). This imports everything from tkinter , but doesn't let you know if something you thought was there actually isn't

from tkinter import *

whereas this

from tkinter import Tkinter

would have immediately pointed out that (the class) Tkinter does not exist in tkinter . Another option that some seem to prefer (incl. myself in some cases), is import tkinter followed by tkinter.Tk() , which has the advantage that it's obvious where a class comes from. Futhermore, PEP8 also discourages the use of star imports (referring to them as "wildcard imports").