Python function-id function

Python function-id function id (object)

Function: the id card number of the object is returned, which is unique and unchanged. However, the same id value may appear in the non-overlapping lifecycle. 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.

Python version: Python2.x Python3.x

Python official English document explanation:

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.

Note: the id value of an object in the CPython interpreter represents its address in the memory (the interpreter implemented in Python C ).

Code example:

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

This id is used to determine whether two objects are equal.

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