Python interview-ternary conditional operator three-mesh operator

The trinocular operator is an important part of C language. The conditional operator is the only operator with three operands, also known as a ternary operator.

In C-style languages, the ternary operator is in the following form:

<span style= "Font-family:arial;font-size:12px;color: #333333;" ><condition>? <expression1>: <expression2></span>

But there is no such operator in Python, and before Python 2.5, you can represent the ternary operator in the following way

<span style= "Font-family:arial;font-size:12px;color: #333333;" > (X, Y) [c]</span>

where c is the condition, if C is not true, then the first element x in the progenitor is returned, and if C is set, then the second element y is returned.

P.S. Not recommended. Because the expression x, Y will execute, and we only need one.

Example:

<span style= "Font-family:arial;color: #333333;" ><span style= "FONT-SIZE:12PX;" >val = float (raw_input (' Age: ')) print ' You should is ', (' working ', ' retired ') [val>65]# resultage:67you should be ret Ired</span></span>

Expression variants:

Age = 15# Selecting an item from a Tupleprint ((' Adult ', ' Kid ') [age <]) # which are the equivalent Of...print (' adult ', ' Kid ') [true]] # Or more explicit by using Dictprint ({True: ' Kid ', False: ' adult '}[age <]) # using Lambdaage = 15print (Lambda: ' Kid ', Lambda: ' adult ') [age >] ()) # using And/orage = 15print (age <) and ' kid ' or ' adult '

Starting with Python 2.5, when Pep 308 was adopted, a single-line if expression was introduced to replace the trinocular operator.

<expression1> if <condition> else <expression2>

In this way, expression 1 is only executed and returned when the condition is set, and Expression 2 is formed and returned. In this way, only one expression is executed and no resources are wasted.

Val=float (Raw_input (' Age: ')) "print ' You should is ', ' retired ' if val>65 Else ' working ' # resultage:76you should be Retired

Use the following code to detect:

Def f1 ():p rint "f1!" Return 1 def f2 ():p rint "f2!" Return 2 if __name__ = = "__main__": v = F1 () if True else F2 () print "V =", v print "-" * v2 = f1 () if False else F2 () pri NT "v2 =", v2    # resultf1!v = 1----------f2!v2 = 2

As we can see, only the F1 method is executed at first, and the second expression executes only the F2 method, and not two methods are executed.

Transformation of ternary expressions

Age = 15print (' Kid ') if-age < Else (' teenager ') if-age <-else (' adult ') # teenager# which is the same as:if age <:    If age <:        print (' Kid ')    else: print (        ' teenager ') Else:    print (' adult ') # teenager

We can use Pprint to check that the ternary expression of Python is from left to right.

From Pprint import pprintpprint (' expression_1 ') if Pprint (' condition_1 ') Else pprint (' expression_2 ') if Pprint (' Condition_2 ') Else pprint (' expression_3 ') # result ' condition_1 ' condition_2 ' expression_3 '

Reference:

http://www.pythoncentral.io/one-line-if-statement-in-python-ternary-conditional-operator/

Http://stackoverflow.com/questions/394809/does-python-have-a-ternary-conditional-operator

http://oldj.net/article/python-ternary-operator/

Python interview-ternary conditional operator three-mesh operator