Ternary Operator in Python

Ternary operators also known as conditional expressions are operators that evaluate something based on a condition being true or false. It was added to Python in version 2.5.
It simply allows to test a condition in a single line replacing the multiline if-else making the code compact.

Syntax :

[on_true] if [expression] else [on_false] 

1. Simple Method to use ternary operator:

   # Program to demonstrate conditional operator a, b = 10, 20    # Copy value of a in min if a < b else copy b min = a if a < b else b    print(min)

   Output: 
   10
   

2. Direct Method by using tuples, Dictionary and lambda

   # Python program to demonstrate ternary operator a, b = 10, 20    # Use tuple for selecting an item print( (b, a) [a < b] )    # Use Dictionary for selecting an item print({True: a, False: b} [a < b])    # lamda is more efficient than above two methods # because in lambda  we are assure that # only one expression will be evaluated unlike in # tuple and Dictionary print((lambda: b, lambda: a)[a < b]())

   Output:
   10
   10
   10
   

3. Ternary operator can be written as nested if-else:

   # Python program to demonstrate nested ternary operator a, b = 10, 20    print ("Both a and b are equal" if a == b else "a is greater than b"         if a > b else "b is greater than a")

   Above approach can be written as:

   # Python program to demonstrate nested ternary operator a, b = 10, 20    if a != b:     if a > b:         print("a is greater than b")     else:         print("b is greater than a") else:     print("Both a and b are equal")

   Output: b is greater than a
   

Important Points:

• First the given condition is evaluated (a < b), then either a or b is returned based on the Boolean value returned by the condition
• Order of the arguments in the operator is different from other languages like C/C++ (See C/C++ ternary operators).
• Conditional expressions have the lowest priority amongst all Python operations.

Method used prior to 2.5 when ternary operator was not present
In an expression like the one given below , the interpreter checks for the expression if this is true then on_true is evaluated, else the on_false is evaluated.

Syntax :

'''When condition becomes true, expression [on_false]
   is not executed and value of "True and [on_true]"
   is returned.  Else value of "False or [on_false]"
   is returned.
   Note that "True and x" is equal to x. 
   And "False or x" is equal to x. '''
[expression] and [on_true] or [on_false] 

Example :

Output:
10

Note : The only drawback of this method is that on_true must not be zero or False. If this happens on_false will be evaluated always. The reason for that is if expression is true, the interpreter will check for the on_true, if that will be zero or false, that will force the interpreter to check for on_false to give the final result of whole expression.

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