[Python] hasattr (), GetAttr (), SetAttr () three relations and application

Hasattr (object, name)

Determines if an object (object) has a Name property or method that returns a Boolean value that has the Name property return True, otherwise false

In [1]: Class Test (object):   ...:     name = ' hkey '   ...:     def hello (self):   ...:         print (' Hello ', Self.name)   : [2]: T = Test () in [3]: Print (hasattr (t, ' name ')) # Note: The property ' name ' is required in quotation marks Truein [4]: Print (hasattr (t, ' Hello ')) # method is also a property of class true

GetAttr (object, name[, default])

Gets the object's property or method (name), if it exists, prints the default value if it is not present, the default value is optional, the default value does not exist the Error object does not have the attribute;

In [1]: Class Test (object):   ...:     name = ' hkey '   ...:     def hello (self):   ...:         print (' Hello ', Self.name): [   2]: t = Test () in [3]: Print (getattr (t, ' name ')) Hkeyin [4]: Print (getattr (t, ' hello ')) <bound met Hod Test.hello of <__main__. Test object at 0x000001499524ee80>>in [5]: Print (getattr (t, ' age '))------------------------------------------- --------------------------------attributeerror                            Traceback (most recent) < Ipython-input-5-bd4a642cfb8c> in <module> ()----> 1 print (getattr (t, ' age ') # without this property or method Attributeerror: ' Test ' object has no attribute ' age ' in [6]: Print (getattr (t, ' age ', 20)) # Set default value 20

SetAttr (object, name, values)

Assigns a value to the object's property, and if the property does not exist, first create the re-assignment

# object does not exist attribute (age), new attribute with SetAttr ' age ' in [1]: Class Test (object):   ...:     name = ' hkey '   ...:     def hello (sel f):   ...:         print (' Hello ', self.name)   ...: in [2]: T = Test () in [3]: Print (hasattr (t, ' age ')) Falsein [4]: Setatt R (T, ' age ', a) in [5]: Print (hasattr (t, "age")) Truein [6]: Print (getattr (t, ' age ')) 20# object existence attribute (name), overwrite original property value with SetAttr In [1]: Class Test (object):   ...:     name = ' hkey '   ...:     def hello (self):   ...:         print (' Hello ', Self.name)   : In [2]: T = Test () in [3]: Print (hasattr (t, ' name ')) # use Hasattr to check if object exists with the ' name ' property, true for existence Truein [4]: SetAttr (t, ' name ', ' Superman ') # SetAttr re-assigns the ' name ' property to ' Superman ' in [5]: Print (getattr (t, ' name ')) # Use GetAttr to get ' nam The value of the E ' property Supermanin [6]: Print (t.name) # directly invokes the Name property of the instance ' t ' Superman

From the above example, it is worth noting that if an object already has a property and again uses SetAttr to assign a value to the property, the property will change.

Hasattr (), GetAttr (), SetAttr () Usage scenarios

* Decoupling the program as a reflection *

In [1]: Class Test (object):   ...:     def __init__ (self):   ...:         self.x = 1   ...:         self.y = 2   ...: c8/> ...:     def sum (self): ...:         print (self.x + self.y)   ...   :     def sub (self):   ... :         print (SELF.X-SELF.Y)   ...: in [2]: T = Test () in [3]: While True:   ...:     cmd = input ('--'). Strip ()   ...:     if hasattr (t, cmd): # ' hasattr ' to determine if ' cmd ' property exists   ...:         func = getattr (t, cmd) # getattr get ' cmd ' genus The value of the sex ...   :         func () # executes this property   ...:     else:   ...:         setattr (t, cmd, t.sum) # If you enter a property name that does not exist, use ' SetAttr ' re-assigned ' cmd ' to ' t.sum ' ...    :         func = getattr (t, cmd)  # GetAttr Get the value of ' cmd ' property ...   :         func () # Execute this property ...   : # execution Result:-->SUM3-->SUB-1-->DDDDDD3

[Python] hasattr (), GetAttr (), SetAttr () three relationships and their use