Class variable not working for some reason? Python

Question

class Note:
     nextseqNum = 0
     def __init__(self):
        self.text        = str
        self.dateCreated = datetime
        self.dateRead    = datetime
        self.description = str
        self.category    = str
        self.priority    = int
        self.hidden      = bool
        self.seqNum      = nextseqNum
        nextseqNum       += 1

For some reason it is throwing me

UnboundLocalError: local variable 'nextseqNum' referenced before assignment

I don't understand why. That is how you make a shared class varaible right?

mgilson · Accepted Answer · 2014-10-01 23:45:57Z

3

The shared class variable needs to be accessed on the class -- It doesn't become a local variable in class methods (which explains the error message):

self.seqNum = Note.nextseqNum
Note.nextseqNum += 1

there are some shortcuts:

self.seqNum = self.nextseqNum  # Not found on self, so looked up on class.
Note.nextseqNum += 1

works because if a name isn't found on an instance, python then looks at the class. If you don't want to name the class explicitly:

self.seqNum = self.__class__.nextseqNum  # for new-style classes, type(self) == self.__class__
self.__class__.nextseqNum += 1

answered Oct 1, 2014 at 23:45

mgilson

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