Introduction to the built-in functions getattr () in Python and examples

In the official Python document: GetAttr () is interpreted as follows:

GetAttr (object, name[, default]) Return the value of the named attribute of object. Name must is a string. The If the string is the name of the one of the object ' s attributes, and the result is the value of this attribute. For example, GetAttr (x, ' Foobar ') are equivalent to X.foobar. If the named attribute does not exist, the default is returned if provided, and otherwise attributeerror is raised.

Returns an object value based on the property name. If "name" is the name of the object property, the value of the corresponding property is returned.

' #-*-coding:utf-8-*-' __author__ = ' Lucas ' class Attrtest (object):  def __init__ (self):    pass  def TRYGETATTR0:    self.name = ' Lucas '    print self.name    #equals    to self.name print getattr (self, ' Name ')  def attribute1 (self,para1):    print ' attribute1 called and ' + para1+ ' is passed in as a parameter '  def TR Ygetattr (self): Fun    = GetAttr (self, ' attribute1 ')    print type ("Fun") Fun    (' crown ') if __name__== ' __main__ ':  test = attrtest ()  print ' GetAttr (self,\ ' name\ ') equals to Self.name '  test.trygetattr0 ()  Print ' attribute1 is indirectly called by Fun () '  test.trygetattr ()  print ' attrribute1 are directly called '  Test.attribute1 (' tomato ')

The result of this code execution is:

GetAttr (self, ' name ') equals to Self.name lucaslucasattribute1 was indirectly called by Fun ()
 
  
   
  attribute1 Called and Crown are passed in as a parameterattrribute1 are directly calledattribute1 called and tomato are passed in as a P Arameterprocess finished with exit code 0
 
  

The first function tryattribute0 () is very well understood, as the definition says. The second function, Tryattribute1 (), is a bit confusing. In fact, the principle is not complicated, we see the fun type is Instancemethod, here you can think: for the function, the return value of GetAttr () is a pointer, the pointer is assigned to the variable to accept it, and then call this variable is equal to the function that calls the variable point.

Principle we know, what is the role of the getattr?

Are you familiar with the reflection in Java or C #? One of the important functions of reflection is to delay loading so that it can be decoupled, which makes the system more efficient to run. As a dynamic language, Python is clearly more powerful in this area,

GetAttr () is a block that implements Python reflection, and in combination with other methods such as SetAttr (), dir (), we can make a lot of interesting things.

Let's look at the following scenario:

1. I need to dynamically add methods from other classes in one class:

#如果类A中有如下方法: Def addnewattributesfromotherclass (self,class_name):    func_names = Dir (class_name) for    func_ Name in Func_names:      if not func_name.startswith ('_'):        new_func = GetAttr (class_name,func_name)        self.__ Setattr__ (Func_name,new_func ())

We only need:

A = a () b = B () A.addnewattributesfromotherclass (b)

So that a can invoke the ' non-private ' method in B.

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