為什么我只需要從模塊導入子類而不從另一個實例導入它的基類和它的屬性？

Question

Python 速成課程：基於項目的實踐編程介紹

讀這本書的時候，我有一個疑問。

為什么我只需要從“admin”導入“Admin”？

在我看來，'test.py' 中的第一行代碼意味着它只復制了類 'Admin' 的代碼。

因此，第二行和第三行代碼不會成功運行，因為它沒有結束代碼塊“from user import User”和類“Privileges”的定義。

任何幫助將不勝感激！

測試文件

from admin import Admin  # line 1


my_admin = Admin('Jade', 'Lam', 'male', '22')  # line 2

my_admin.privileges.show_privileges()  # line 3
print('\n')

管理文件

from user import User


class Admin(User):
    def __init__(self, first_name, last_name, sex, age):
        super().__init__(first_name, last_name, sex, age)
        self.privileges = Privileges()


class Privileges():
    def __init__(self):
        self.privileges = ['can add post', 'can delete post',
                           'can ban user']

    def show_privileges(self):
        print("Admin's privileges: ")
        for privilege in self.privileges:
            print("--" + privilege)

用戶.py

class User():
    def __init__(self, first_name, last_name, sex, age):
        self.first_name = first_name.title()
        self.last_name = last_name.title()
        self.sex = sex
        self.age = age

    def describe_user(self):
        --snip--

    def greet_user(self):
        --snip--

Answer 1

請參閱下面的示例。

# Consider this module:

# mod1.py:
# some outer level code
# gets executed

pass

# functions get defined but do not execute
# unless called from above


def f1():
    pass


def f2():
    pass


# classes get defined and actually execute but
# if they only have defs, again those get defined
# but don't run.


class A:
    pass


class B:
    pass


class C:
    pass


# now main.py:
# mod1 executes. Every name of mod1 also becomes  available
# under the prefix 'mod1.' This is like creating a mod1 namespace
# in outer scope of main.
import mod1

# mod1 only runs once on imports in this module, so this time it won't
# (it already has).
# While you can still access every name from mod1 using the mod1 prefix
# from the above import, below only the A name is kept in the outer scope
# of main.
from mod1 import A

# If A has dependencies on other mod1 names, that does not matter here.
# Those dependencies were solved on mod1 run, and all the names involved
# were accessed as needed at mod1 runtime. These names are actually in a
# different scope that belongs to mod1.

# After imports, main can have mod1 names in its scope, but mod1 never
# had access to main names. Unless it imports main, something it should
# not do to avoid circular imports.

希望你現在明白了。