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3.7 id()
In Python, each object is assigned a unique object identifier (id). An assignment operator associates a variable with
the object on the right-hand side. The object on the right-hand side of the assignment operator may be the result of
evaluating an expression.
The function id() yields the unique object identifier of an object. For example,
>>> id(10)
140709242827296
>>> num = 10
>>> id(num)
Note that object 10 is assigned the object id 140709242827296. On execution of the assignment statement, num
= 10, Python associates the object id 140709242827296 with the variable num. We would like to emphasize
that an object id relates to an instance of executing an instruction. If you invoke IDLE multiple times, id(10) is likely
to yield different object ids.
Next, consider:
>>> num1 = 10
>>> id(num1)
140709242827296
It is interesting to note that each of the variables num and num1 is associated with the same object 10 of type int
(numeric values), and both have the same id. Next, consider:
>>> num1 = 12
>>> id(num1)
140709242827360
>>> id(num)
140709242827296
As expected, the variable num1 now gets associated with the new object 12. The variable num continues to be
associated with object 10. Next, let us consider:
>>> num = 12.4
>>> id(num)
2489891082064
Note that on the execution of the assignment statement, num = 12.4, Python associates the variable num with
the floating-point object 12.4 having object id 2489891082064.
It is interesting to note that Python may (not necessarily) create different objects for the same value. For example,
>>> id(12.4)
2489862941840
>>> id(12.4)
2489895421264
>>> id(234)
140709242834464
>>> id(234)
140709242834464
Typically, a short integer in Python gets associated with a fixed object id, but the same may not be true in the case of
more complex objects like floating-point numbers.
3.8 L-value and R-Value
Consider the following assignment statement:
sum = x+20
Basics of Python Programming 51

