Python Error "name 'A' is not defined" in class variable initialization

Question

This code works in the python command line. However, when compiling it in a module it gives the following error: "name 'A' is not defined."

>>> class A:
...     a = 2
...     c = A.a
... 
>>> A.c
2

class A:
    a = 2
    c = A.a

NameError: name 'A' is not defined

I found a better solution. As shown below, a static variable is available for the initialization of another static variable. The code below compiles fine.

class A:
    a = 2
    b = a

c = A()
print(c.b)

The name A isn't defined until after the class block is finished. So you can't reference it while defining the class. — Barmar
– Barmar, Commented Jan 25, 2022 at 22:08
I suspect in your interactive session you had previously defined the A class. So you were using the old value of A.a. — Barmar
– Barmar, Commented Jan 25, 2022 at 22:08
Ok, that makes sense. But, why does it work in the command line? — Geoff
– Geoff, Commented Jan 25, 2022 at 22:13
@Barmar Thanks. You are correct. I reset my command line, and then it generated the same error. — Geoff
– Geoff, Commented Jan 25, 2022 at 22:16

XxJames07- · Accepted Answer · 2022-01-25 22:14:17Z

2

this is b/c the class is not defined yet, so you have to put the c = A.a outside of the class, or you could do:

 class A:
     a = 2
 c = A.a
 print(c)

Output:

or, as @Barman replied, you could do also:

 class A:
     a = 2
 A.c = A.a
 print(A.c)

Out:

edited Jan 25, 2022 at 22:14

answered Jan 25, 2022 at 22:10

XxJames07-

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2 Comments

Barmar Over a year ago

Or A.c = A.a to do what he was trying to do.

Geoff Over a year ago

@Barmar Ya, I get it now. I need to define a class variable without initializing it. Then, if I want to use the other class variables to assign to this class variable, I can do later in my code by using the class name like this: A.b = A.a.

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