我有下面的代碼片段,可以創建一個筆記并添加到筆記本中.

我的問題與全局變量last_id更相關.當我將它聲明為類變量時,即在Class Note中,我得到以下錯誤但是當我在類外聲明時,我的代碼工作正常.

以下是我的澄清：

>為什么不接受類變量.

>當我在函數中將其聲明為全局變量時,為什么需要定義last_id？

錯誤：

C:\Python27\Basics\OOP\formytesting>python notebook.py

Traceback (most recent call last):

File "notebook.py", line 38, in

firstnote = Note('This is my first memo','example')

File "notebook.py", line 10, in __init__

last_id += 1

NameError: global name 'last_id' is not defined

code.py

import datetime

last_id = 0

class Note:

def __init__(self, memo, tags):

self.memo = memo

self.tags = tags

self.creation_date = datetime.date.today()

global last_id

last_id += 1

self.id = last_id

#global last_id

#last_id += 1

#self.id = last_id

def __str__(self):

return 'Memo={0}, Tag={1}, id={2}'.format(self.memo, self.tags,self.id)

class NoteBook:

def __init__(self):

self.notes = []

def add_note(self,memo,tags):

self.notes.append(Note(memo,tags))

def __iter__(self):

for note in self.notes:

yield note

if __name__ == "__main__":

firstnote = Note('This is my first memo','example')

print(firstnote)

Notes = NoteBook()

print("Adding a new note object")

Notes.add_note('Added thru notes','example-1')

Notes.add_note('Added thru notes','example-2')

for note in Notes.notes:

print(note.memo,note.tags)

for note in Notes:

print(note)

print("Adding a new note object----End")

總結

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