In Python, what is the id () function, and pythonid function?

In Python, what is the id () function, and pythonid function?

What is the explanation in the Python official documentation?

Id (object)
Return the "identity" of an object. this is an integer (or long integer) which is guaranteed to be unique and constant for this object during its lifetime. two objects with non-overlapping lifetimes may have the same id () value.
CPython implementation detail: This is the address of the object in memory.

We can see that:

1. The id (object) returns the "id card number" of the object, which is unique and unchanged. However, the same id value may appear in the lifecycle that does not overlap. The object mentioned here should be a composite type object (such as class and list). For string and integer types, the variable id changes with the value.

2. The id value of an object in the CPython interpreter represents its address in the memory. (CPython Interpreter: http://zh.wikipedia.org/wiki/CPython)

class Obj():  def __init__(self,arg):   self.x=arg if __name__ == '__main__':  obj=Obj(1)  print id(obj)  #32754432  obj.x=2  print id(obj)  #32754432  s="abc"  print id(s)   #140190448953184  s="bcd"  print id(s)   #32809848  x=1  print id(x)   #15760488  x=2  print id(x)   #15760464 

In addition, the id value is used to determine whether two objects are equal.

class Obj():  def __init__(self,arg):   self.x=arg  def __eq__(self,other):   return self.x==other.x if __name__ == '__main__':  obj1=Obj(1)  obj2=Obj(1)  print obj1 is obj2 #False  print obj1 == obj2 #True  lst1=[1]  lst2=[1]  print lst1 is lst2 #False  print lst1 == lst2 #True  s1='abc'  s2='abc'  print s1 is s2  #True  print s1 == s2  #True  a=2  b=1+1  print a is b  #True  a = 19998989890  b = 19998989889 +1  print a is b  #False 

The difference between is and = is that is a comparison in memory, while = is a comparison of values.

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