Look at me first yeah Java A popular understanding of the reflection mechanism in ： There is one in the reflection “ back ” The concept of , So if you want to explain reflection, you have to start with “ just ” Start explaining , generally speaking , When a user uses a class , You should know this class first , Then the instantiated object is generated through this class , however “ back ” It refers to finding classes through objects .
And for Python, If we need to import modules dynamically , And dynamically access the properties and methods in the object , How do you do it? ？ Look at the code below .
s = "lib.test.commons"
m1 = __import__(s) # This only dynamically imports lib modular
m2 = __import__(s, fromlist = True) # fromlist = True, In this way, you can dynamically import by path commons modular
inp_func = input(" Please enter the function to execute ：")
f = getattr(m2, inp_func)() # Add "()" Dynamically executing functions
It can be seen from the above , Reflection is ：
hasattr(obj,name)
Judge an object obj Is there any name Property or name Method , return bool value , Yes name Property return True, Otherwise return to False.
It should be noted that name Wrap it in quotation marks .
class test():
name="xiaohua"
def run(self):
return "HelloWord"
>>> t=test()
>>> hasattr(t, "name") # The objects of judgment are name attribute
True>>> hasattr(t, "run") # The objects of judgment are run Method
True
getattr(obj,name[,default])
Get objects obj Property or method , If it exists, print it out , If it doesn't exist , Default values are printed , The default value is optional .
It should be noted that , If it's the method of the returned object , The memory address of the method is returned , If you need to run this method , You can add a pair of parentheses after it .
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class test():
name="xiaohua"
def run(self):
return "HelloWord"
>>> t=test()
>>> getattr(t, "name") # obtain name attribute , Print out the existence .
'xiaohua'
>>> getattr(t, "run") # obtain run Method , If it exists, print out the memory address of the method .
<bound method test.run of <__main__.test instance at 0x0269C878>>
>>> getattr(t, "run")() # obtain run Method , Back plus "()" You can run this method .
'HelloWord'
>>> getattr(t, "age") # Get a nonexistent property .
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: test instance has no attribute 'age'
>>> getattr(t, "age","18") # If the attribute does not exist , Returns a default value .
'18'
setattr(obj,name,values）
To object obj Property of , If the attribute does not exist , Create first, then assign .
class test():
name="xiaohua"
def run(self):
return "HelloWord"
>>> t=test()
>>> hasattr(t, "age") # Judge whether the attribute exists
False
>>> setattr(t, "age", "18") # Property is created when it does not exist , And assignment , But no return value
>>> hasattr(t, "age") # Attributes exist
True
delattr(obj,name)
Delete object properties .
in addition ,eval() and exec() Functions are also reflection functions .
