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Python switch statement

The simplest way to imitate case statement in Python is to use if elif... construct.  The main drawback is that expression that  selected the code  block might be  evaluated multiple time, but you can factor this out of if.

In C: 
switch(n) {
  case 0:
    printf("You typed zero.\n");
    break;
  case 1:
  case 9:
    printf("n is a perfect square\n");
    break;
  case 2:
    printf("n is an even number\n");
  case 3:
  case 5:
  case 7:
    printf("n is a prime number\n");
    break;
  case 4:
    printf("n is a perfect square\n");
  case 6:
  case 8:
    printf("n is an even number\n");
    break;
  default:
    printf("Only single-digit numbers are allowed\n");
  break;
}

In Python: 


if n == 0:
    print "You typed zero.\n"
elif n== 1 or n == 9 or n == 4:
    print "n is a perfect square\n"
elif n == 2:
    print "n is an even number\n"
elif  n== 3 or n == 5 or n == 7:
    print "n is a prime number\n"
 
 
 
options = {0 : zero,
                1 : sqr,
                4 : sqr,
                9 : sqr,
                2 : even,
                3 : prime,
                5 : prime,
                7 : prime,
}
 
def zero():
    print "You typed zero.\n"
 
def sqr():
    print "n is a perfect square\n"
 
def even():
    print "n is an even number\n"
 
def prime():
    print "n is a prime number\n"
 



 

           
                  The python if statements start to look a lot nicer (for this example) when you use `in`. I 
                  also took the liberty of removing the extra ‘\n’ since it isn’t necessary with 2.x’s print statement:
if n == 0:
    print "You typed zero."
elif n == 2:
    print "n is an even number"
elif n in (1, 9, 4)
    print "n is a perfect square"
elif  n in (3, 5, 7):
    print "n is a prime number"

              
         

Wrapping the entire thing in a single-execution loop (e.g. a while loop which sets its condition to false on the first line) 
makes it quite easy to break out from it, though that might not be very “Pythonic”. A little more planning re: mutually exclusive 
options and you could reduce the number of checks that have to get made every time the code is run. However, at the end of the day, 
if you are concerned about performance, do it in C

              
         




   

      
      

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[Nov 14, 2019]  How to implement  a switch-case statement in Python by Sreeram Sceenivasan





Oct 24, 2017 |  jaxenter.com

 

   
...You can use it to execute different blocks of code, depending on the variable value during runtime. Here's an example of a 
   switch statement in Java.


   
public static void switch_demo(String[] args) {
 
        int month = 8;
        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);
}




   
Here's how it works:

   
    

      
  1. Compiler generates a jump table for switch case statement
    2. 

      
  2. The switch variable/expression is evaluated once
    3. 

      
  3. Switch statement looks up the evaluated variable/expression in the jump table and directly decides which code block to execute.
    4. 

      
  4. If no match is found, then the code under default case is executed
    5. 
   


   
In the above example, depending on the value of variable month , a different message will be displayed in the standard 
   output. In this case, since the month=8, 'August' will be printed in standard output.

    Read also:
   
   An introduction to the Python programming language

   
When Guido van Rossum developed Python, he wanted to create a "simple" programming language that bypassed the vulnerabilities 
   of other systems. Due to the simple syntax and sophisticated syntactic phrases, the language has become the standard for various 
   scientific applications such as machine learning. Switch statements


   
Although popular languages like Java and PHP have in-built switch statement, you may be surprised to know that Python language 
   doesn't have one. As such, you may be tempted to use a series of if-else-if blocks, using an if condition for each case of your switch 
   statement.


   
However, because of the jump table, a switch statement is much faster than an if-else-if ladder. Instead of evaluating each condition 
   sequentially, it only has to look up the evaluated variable/expression once and directly jump to the appropriate branch of code to 
   execute it.

   SEE MORE: Python jumps past Java, Javascript 
   is still most popular language for GitHubbers

   
How to implement switch statement in Python 


   
The Pythonic way to implement switch statement is to use the powerful dictionary mappings, also known as associative arrays, that 
   provide simple one-to-one key-value mappings.


   
def switch_demo(argument):
switcher = {
  1: "January",
  2: "February",
  3: "March",
  4: "April",
  5: "May",
  6: "June",
  7: "July",
  8: "August",
  9: "September",
  10: "October",
  11: "November",
  12: "December"
}
print switcher.get(argument, "Invalid month")



   
Here's the Python implementation of the above switch statement. In the following example, we create a dictionary named switcher 
   to store all the switch-like cases.


   
In the above example, when you pass an argument to the switch_demo function, it is looked up against the switcher 
   dictionary mapping. If a match is found, the associated value is printed, else a default string ('Invalid Month') is printed. The 
   default string helps implement the 'default case' of a switch statement.

   Dictionary mapping for functions

   
Here's where it gets more interesting. The values of a Python dictionary can be of any data type. So you don't have to confine 
   yourself to using constants (integers, strings), you can also use function names and lambdas as values.


   
For example, you can also implement the above switch statement by creating a dictionary of function names as values. In this case,
   switcher is a dictionary of function names, and not strings.


   
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()




   
Although the above functions are quite simple and only return strings, you can use this approach to execute elaborate blocks of 
   code within each function.


   
... ... ... 

   

















[Nov 10, 2019] How to implement 
a switch-case statement in Python by Sreeram Sceenivasan




   
 Oct 24, 2017| jaxenter.com


   
...You can use it to execute different blocks of 
   code, depending on the variable value during runtime. Here's an example of a switch statement in Java.


   
public static void switch_demo(String[] args) {
 
        int month = 8;
        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);
}




   
Here's how it works:

   
    

      
  1. Compiler generates a jump table for switch case statement
    2. 

      
  2. The switch variable/expression is evaluated once
    3. 

      
  3. Switch statement looks up the evaluated variable/expression in the jump table and directly decides which code block to execute.
    4. 

      
  4. If no match is found, then the code under default case is executed
    5. 
   


   
In the above example, depending on the value of variable month , a different message will be displayed in the standard 
   output. In this case, since the month=8, 'August' will be printed in standard output.

    Read also:
   
   An introduction to the Python programming language

   
When Guido van Rossum developed Python, he wanted to create a "simple" programming language that bypassed the vulnerabilities 
   of other systems. Due to the simple syntax and sophisticated syntactic phrases, the language has become the standard for various 
   scientific applications such as machine learning. Switch statements


   
Although popular languages like Java and PHP have in-built switch statement, you may be surprised to know that Python language 
   doesn't have one. As such, you may be tempted to use a series of if-else-if blocks, using an if condition for each case of your switch 
   statement.


   
However, because of the jump table, a switch statement is much faster than an if-else-if ladder. Instead of evaluating each condition 
   sequentially, it only has to look up the evaluated variable/expression once and directly jump to the appropriate branch of code to 
   execute it.


   









SEE MORE: Python jumps past Java, Javascript 
   is still most popular language for GitHubbers

   How to implement switch statement in Python

   
The Pythonic way to implement switch statement is to use the powerful dictionary mappings, also known as associative arrays, that 
   provide simple one-to-one key-value mappings.


   
def switch_demo(argument):
switcher = {
  1: "January",
  2: "February",
  3: "March",
  4: "April",
  5: "May",
  6: "June",
  7: "July",
  8: "August",
  9: "September",
  10: "October",
  11: "November",
  12: "December"
}
print switcher.get(argument, "Invalid month")



   
Here's the Python implementation of the above switch statement. In the following example, we create a dictionary named switcher 
   to store all the switch-like cases.


   
In the above example, when you pass an argument to the switch_demo function, it is looked up against the switcher 
   dictionary mapping. If a match is found, the associated value is printed, else a default string ('Invalid Month') is printed. The 
   default string helps implement the 'default case' of a switch statement.

   Dictionary mapping for functions

   
Here's where it gets more interesting. The values of a Python dictionary can be of any data type. So you don't have to confine 
   yourself to using constants (integers, strings), you can also use function names and lambdas as values.


   
For example, you can also implement the above switch statement by creating a dictionary of function names as values. In this case,
   switcher is a dictionary of function names, and not strings.


   
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()




   
Although the above functions are quite simple and only return strings, you can use this approach to execute elaborate blocks of 
   code within each function.


   
... ... ... 





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Last modified: November 14, 2019