A switch case statement in a computer Programming Language is a powerful tool that gives the programmer total control over the flow of the program according to the outcomes of an expression or a variable. Switch cases are particularly used to execute a different block of codes in relation to the results of expression during the program run time.
The program takes a certain course if the result is a certain value and another course if the result is another value and so on and so forth.
Let me begin by showing you how a switch case statement functions in Java so that you have a clue of what to expect in the Python switch case statement, although it could be different in the way they have implemented, the concept remains the same.
To Follow Up this Tutorial You can you use Any of your Favourite Python IDE or Code Editors.
Java switch case demo of how to switch between months of the year and provide a default result if no match is found in the switch statement.
public static void switch_demo(String[] args) {
int month = 7;
String monthString;
switch (month) {
case 1: monthString = "January";
break;
case 2: monthString = "February";
break;
case 3: monthString = "March";
break;
case 4: monthString = "April";
break;
case 5: monthString = "May";
break;
case 6: monthString = "June";
break;
case 7: monthString = "July";
break;
case 8: monthString = "August";
break;
case 9: monthString = "September";
break;
case 10: monthString = "October";
break;
case 11: monthString = "November";
break;
case 12: monthString = "December";
break;
default: monthString = "Invalid month";
break;
}
System.out.println(monthString);
}
Let’s break down the above switch case statement:
Step 1: The compiler first generates a jump table for the switch statement
Step 2: The switch statement evaluates the variable or the expression only once.
Step 3: The switch statement looks upon the evaluated result and makes a decision based on the result on which block of code to execute.
Guido Van Rossum a Python developer believed in a simple programming language that could bypass the system vulnerabilities and hitches found in other programming languages, he wanted to create a simple syntax with more sophisticated syntactic phrases.
He never imagined that today, Python programming language could be the programming language to look up to when it comes to the standard language for designing scientific machine learning applications.
Switch case examples in Python
Python doesn’t have built-in switch statements like you could find programming languages like PHP and Java does, instead, as a Python programmer you could be tempted to use if-else-if blocks, but switch cases are efficient to use because of jump table than the if-else-if ladder.
The reason for this is, instead of evaluating each condition in a sequential manner, it looks at the evaluated expression or variable and jumps directly to the relevant branch of code to execute.
Switch using an if-else-if ladder to find the surface area, literal area, and volume of a cylinder.
def switch():
r = int(input("Enter Radius : "))
h = int(input("Enter Height : "))
print("Press 1 for Surface Area \npress 2 for Literal Area \npress 3 for Volume \n")
option = int(input("your option : "))
if option == 1:
result = 2*3.17*r*(r+h)
print("\nSurface Area Of Cylinder = ",result)
elif option == 2:
result = 2 * 3.17 * r * h
print("Literal Area Of Cylinder = ", result)
elif option == 3:
result = 3.17*r*r*h
print("Volume Of Cylinder = ", result)
else:
print("Incorrect option")
switch()
Explanation: In the example above, if the option is 1, the surface area of a cylinder is calculated if the option is 2, the literal surface area is calculated and finally option 3, the volume of the cylinder is calculated.
Switch case statement using class to convert literal to string ‘month’
class PythonSwitchStatement:
def switch(self, month):
default = "Invalid month"
return getattr(self, 'case_' + str(month), lambda: default)()
def case_1(self):
return "January"
def case_2(self):
return "February"
def case_3(self):
return "March"
def case_4(self):
return "April"
def case_5(self):
return "May"
def case_6(self):
return "June"
def case_7(self):
return "July"
def case_8(self):
return "August"
def case_9(self):
return "September"
def case_10(self):
return "October"
def case_11(self):
return "November"
def case_12(self):
return "December"
s = PythonSwitchStatement()
print(s.switch(1))
print(s.switch(3))
print(s.switch(13))
The output will be:
___________________
January
March
Invalid month
___________________
Explanation: First, create a class called
PythonSwitchStatementThe
switch()getattr() If it doesn’t find a match, the
getattr()Dictionary mapping replacement
# Function to convert number into string
# Switcher is dictionary data type here
def numbers_to_strings(argument):
switcher = {
0: "zero",
1: "one",
2: "two",
}
# get() method of dictionary data type returns
# value of passed argument if it is present
# in dictionary otherwise the second argument will
# be assigned as the default value of the passed argument
return switcher.get(argument, "nothing")
# Driver program
if __name__ == "__main__":
argument=0
print numbers_to_strings(argument)
Example using Dictionary mapping for functions by Switcher
def one():
return "January"
def two():
return "February"
def three():
return "March"
def four():
return "April"
def five():
return "May"
def six():
return "June"
def seven():
return "July"
def eight():
return "August"
def nine():
return "September"
def ten():
return "October"
def eleven():
return "November"
def twelve():
return "December"
def numbers_to_months(argument):
switcher = {
1: one,
2: two,
3: three,
4: four,
5: five,
6: six,
7: seven,
8: eight,
9: nine,
10: ten,
11: eleven,
12: twelve
}
# Get the function from switcher dictionary
func = switcher.get(argument, lambda: "Invalid month")
# Execute the function
print func()
Example using a dictionary mapping to return value
b ={
'a' : 122,
'b' : 123,
'c' : 124,
'd' : 125
}
# take user input
inp = input('input a character : ')
# -1 is the default value if there are no keys that match the input
print('The result for inp is : ', b.get(inp, -1))
Using dictionary mapping to switch the days of the week
def week(i):
switcher={
0:'Sunday',
1:'Monday',
2:'Tuesday',
3:'Wednesday',
4:'Thursday',
5:'Friday',
6:'Saturday'
}
return switcher.get(i, "Invalid day of the week")
Then make calls to
week() i.e
week(2)week(4)week(5.5)Conclusion
Python does not have an in-built switch-case construct, but you can use dictionary mapping instead in place of switch case.
Python developer did not include the switch-case construct for a good reason.
Although many programmers and developers have been pushing for the inclusion of switch case construct in Python, whether their proposal will be considered or not, Python switch case alternatives serve even better.
(Originally published here)