Python Switch case

Python Switch Case Statement

Unlike other programming languages, Python doesn’t provide a switch case instrument over the self.

However, it has many other constructs like a dictionary, lambda function, and classes to write a custom implementation of the Python switch case statement.

If you are keen to know why Python doesn’t have a switch case, then do refer the explanation at PEP 3103.

Before diving into further, let’s have a quick view of the most common example of a switch case statement in the C programming language.

A Typical Switch Case in C Programming

• In C, you can only pass an integer or enum value to the switch-case statement.

• Unlike the if…else block which requires evaluating expressions in each condition, the switch has a single point of interaction which leads to different paths of execution.

• A switch is a control instruction which decides the control to flow based on the value of a variable or an expression.

In the below example, the variable ‘dayOfWeek’ is a constant integer variable which represents days in a week. And the switch-case block prints the name of the day based on its value.

    switch (dayOfWeek) {
    case 1:
        printf("%s", Monday);
        break;
    case 2:
        printf("%s", Tuesday);
        break;
    case 3:
        printf("%s", Wednesday);
        break;
    case 4:
        printf("%s", Thursday);
        break;
    case 5:
        printf("%s", Friday);
        break;
    case 6:
        printf("%s", Saturday);
        break;
    case 7:
        printf("%s", Sunday);
        break;
    default:
        printf("Incorrect day");
        break;
    }

There are a couple of facts to consider for the switch-case statement.

• The expression under the switch gets evaluated once.

• It should result in a constant integer value. [Note: In Python, we can alter this behavior.]

• A case with a duplicate value should not appear.

• If no case matches, then the default case gets executed.

Implement Python Switch Case Statement

Switch Case using a Dictionary

It is simple to use a dictionary for implementing the Python switch case statement. Follow the below steps.

• First, define individual functions for every case.

• Make sure there is a function/method to handle the default case.

• Next, make a dictionary object and store each of the function beginning with the 0th index.

• After that, write a switch() function accepting the day of the week as an argument.

• The switch() calls the get() method on the dictionary object which returns the function matching the argument and invokes it simultaneously.

# Implement Python Switch Case Statement using Dictionary

def monday():
    return "monday"
def tuesday():
    return "tuesday"
def wednesday():
    return "wednesday"
def thursday():
    return "thursday"
def friday():
    return "friday"
def saturday():
    return "saturday"
def sunday():
    return "sunday"
def default():
    return "Incorrect day"

switcher = {
    1: monday,
    2: tuesday,
    3: wednesday,
    4: thursday,
    5: friday,
    6: saturday,
    7: sunday
    }

def switch(dayOfWeek):
    return switcher.get(dayOfWeek, default)()

print(switch(1))
print(switch(0))

The output is as follows:

Monday
Incorrect day

Switch Case using a Class

It is quite easy to use a class for implementing the Python switch case statement. Let’s do it with an example.

• In the below example, there is a PythonSwitch class which defines the switch() method.

• It takes the day of the week as an argument, converts it to string and appends to the ‘case_’ literal. After that, the resultant string gets passed to the getattr() method.

• The getattr() method returns a matching function available in the class.

• If the string doesn’t find a match, then the getattr() returns the lambda function as default.

• The class also have the definition for functions specific to different cases.

# Implement Python Switch Case Statement using Class

class PythonSwitch:

    def switch(self, dayOfWeek):
        default = "Incorrect day"
        return getattr(self, 'case_' + str(dayOfWeek), lambda: default)()

    def case_1(self):
        return "Monday"
 
    def case_2(self):
        return "Tuesday"
 
    def case_3(self):
        return "Wednesday"

s = PythonSwitch()

print(s.switch(1))
print(s.switch(0))

The output is as follows:

Monday
Incorrect day