Elegant python-scope and lookup strategies

First understand what a namespace is, a namespace is a "named-and-object" mapping, implemented in Python with Dict.

The scope, however, refers to namespaces that can be accessed directly.

When we access a variable, we will follow the order of LEGB to lookup:

• L->local. That is, local variables, such as variables defined in def or lambda.
• E-> enclosing function locals. That is, the variable in the closure.
• G->global (module). Global variables.
• B->built-in. Built-in variables, such as Len ()/keyerror.

When we access an attribute through an instance, self.x, its lookup order is:

• Instance Properties
• Class properties
• The parent class property. By MRO (method resolution Order)

Give a chestnut a more intuitive point. [Python]View Plaincopy

2. s = ' global '
4. Class Foo (object):
6. s = ' class '
8. def __init__ (self):
10. print s #全局变量, output global
12. print Foo.s #类属性, Output class
14. print self.s #实例属性中没找到, so look in the class attribute, output class
16. Self.s = ' instance '#创建了个实例属性
18. print self.s #实例属性能找到, output instance
22. Foo ()

Elegant python-scope and lookup strategies