[英]Python global variable and class functionality
Im creating a simple python program that gives basic functionality of an SMS_Inbox. 我创建了一个简单的python程序,它提供了SMS_Inbox的基本功能。 I have created an SMS_Inbox method.
我创建了一个SMS_Inbox方法。
store = []
message_count = 0
class sms_store:
def add_new_arrival(self,number,time,text):
store.append(("From: "+number, "Recieved: "+time,"Msg: "+text))
**message_count += 1**
def delete(self,i):
if i > len(store-1):
print("Index does not exist")
else:
del store[i]
message_count -= 1
In the bolded bit I am getting an error: 在粗体位我得到一个错误:
UnboundLocalError: local variable 'message_count' referenced before assignment.
I created a global variable store which is an empty list and this works when I use the add_new_variable object. 我创建了一个全局变量存储,它是一个空列表,这在我使用add_new_variable对象时有效。 However for some reason it is not adding values to my global message_count variable.
但是由于某种原因,它没有向我的全局message_count变量添加值。
Please help 请帮忙
That's not how classes work. 这不是班级的工作方式。 Data should be stored within the class instance, not globally.
数据应存储在类实例中,而不是全局存储。
class SMSStore(object):
def __init__(self):
self.store = []
self.message_count = 0
def add_new_arrival(self,number,time,text):
self.store.append(("From: "+number, "Recieved: "+time,"Msg: "+text))
self.message_count += 1
def delete(self, i):
if i >= len(store):
raise IndexError
else:
del self.store[i]
self.message_count -= 1
sms_store = SMSStore()
sms_store.add_new_arrival("1234", "now", "lorem ipsum")
try:
sms_store.delete(20)
except IndexError:
print("Index does not exist")
print sms_store.store
# multiple separate stores
sms_store2 = SMSStore()
sms_store2.add_new_arrival("4321", "then", "lorem ipsum")
print sms_store2.store
If the variable you are referring to is message_count
, the error is because in Python, you have to specify a variable as global
before you can make edits with it. 如果您引用的变量是
message_count
,则错误是因为在Python中,您必须先将变量指定为global
变量,然后才能对其进行编辑。
This should work. 这应该工作。
store = []
message_count = 0
class sms_store:
def add_new_arrival(self,number,time,text):
global message_count
store.append(("From: "+number, "Recieved: "+time,"Msg: "+text))
message_count += 1
def delete(self,i):
if i > len(store-1):
print("Index does not exist")
else:
global message_count
del store[i]
message_count -= 1
As written above, you'd be better off encapsulating it in the __init__
function instead of declaring it global
. 如上所述,最好将其封装在
__init__
函数中,而不是将其声明为global
函数。
You are trying to assign to a global variable message_count
without declaring it as such: 您正在尝试分配给全局变量
message_count
而不声明它:
message_count = 0
class sms_store:
def add_new_arrival(self,number,time,text):
store.append(("From: "+number, "Recieved: "+time,"Msg: "+text))
global message_count
message_count += 1
Try to avoid using globals, or at least encapsulate the variable as a class attribute: 尽量避免使用全局变量,或者至少将变量封装为类属性:
class sms_store:
message_count = 0
store = []
def add_new_arrival(self,number,time,text):
sms_store.append(("From: "+number, "Recieved: "+time,"Msg: "+text))
sms_store.message_count += 1
However, your class instances have no state anymore, so there is no point in creating a class here. 但是,您的类实例不再具有状态,因此在此处创建类没有意义 。 It only serves to confuse your purpose.
它只会混淆你的目的。
Either store state in instances, or use global functions (so don't use a class at all); 要么在实例中存储状态,要么使用全局函数(所以根本不要使用类); the former is preferable to the latter.
前者优于后者。
Transforming your setup to a class whose instances hold state, using proper PEP-8 styleguide naming and string formatting: 使用正确的PEP-8 styleguide命名和字符串格式将您的设置转换为实例保持状态的类:
class SMSStore(object):
def __init__(self):
self.store = []
self.message_count = 0
def add_new_arrival(self, number, time, text):
self.store.append('From: {}, Received: {}, Msg: {}'.format(number, time, text))
self.message_count += 1
You are then free to create one instance and use that as a global if needs be: 然后,您可以自由创建一个实例,并在需要时将其用作全局实例:
sms_store = SMSStore()
Other code just uses sms_store.add_new_arrival(...)
, but the state is encapsulated in one instance. 其他代码只使用
sms_store.add_new_arrival(...)
,但状态封装在一个实例中。
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