Basic Python programming

L-value and R-Value

An lvalue (locator value) represents an object that occupies some identifiable

location in memory (i.e. has an address). rvalues are defined by exclusion. Every

expression is either an lvalue or an rvalue, so, an rvalue is an expression that does not

represent an object occupying some identifiable location in memory.

(a) A left value or l-value is an assignable object. It is any expression that may occur on

the leftside of an assignment. Variables are obvious l-values, but so are items in lists.

(b) A right value or r-value is any expression that has a value that may appear on the

right of an assignment. In python, everything is an r-value.

(c) Traditionally, the underscore ( ) is used as a place-holder for an l-value when we

don't care about the result of the assignment.

(d) In assignment, a tuple of l-values is, itself an l-value:

>>> (a,b,c) = (1,2,3)

>>> a,b,c = 1,2,3

>>> (a,b),_,c = (1,2,),9,3

Each of these effectively assigns a=1, b=2, and c=3.