NameError: name 'Class' is not defined

Question

编译时出现此错误：

Traceback (most recent call last):
  File "c:/Users/dvdpd/Desktop/ProjectStage/Main.py", line 1, in <module>
    class Main:
  File "c:/Users/dvdpd/Desktop/ProjectStage/Main.py", line 6, in Main
    test = Reading()
NameError: name 'Reading' is not defined

代码：

class Main:
    print("Welcome.\n\n")
    test = Reading()
    print(test.openFile)


class Reading:
    def __init__(self):
        pass

    def openFile(self):
        f = open('c:/Users/dvdpd/Desktop/Example.txt')
        print(f.readline())
        f.close()

我无法使用 class Reading，我也不知道为什么。 Main 和 Reading 在同一个文件中，所以我认为我不需要 import.

Answer 1

Python 源文件由解释器从上到下解释。

因此，当您在 class Main 中调用 Reading() 时，它还不存在。您需要交换声明以将 Reading 放在 Main.

之前

Answer 2

您需要在Main

之前定义Reading

Answer 3

您需要在class Main之前定义class Reading。

class Reading:
    def __init__(self):
        pass

    def openFile(self):
        f = open('c:/Users/dvdpd/Desktop/Example.txt')
        print(f.readline())
        f.close()


class Main:
    print("Welcome.\n\n")
    test = Reading()
    print(test.openFile())

Answer 4

前向声明在 Python 中不起作用。因此，仅当您创建 Main class 的对象时才会出现错误，如下所示：

class Main:
    def __init__(self):
        print("Welcome.\n\n")
        test = Reading()
        print(test.openFile)

# Main() # This will NOT work

class Reading:
    def __init__(self):
        pass

    def openFile(self):
        f = open('c:/Users/dvdpd/Desktop/Example.txt')
        print(f.readline())
        f.close()

# Main() # This WILL work

NameError: name 'Class' is not defined

NameError: name 'Class' is not defined

python

nameerror

python-3.x