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Recursion

Recursion in Python is when a function calls itself. It's a useful technique for solving complex problems by breaking them down into smaller parts. The key elements of recursion are the base case (the termination condition) and the recursive case (where the function calls itself).


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def print_message(message, times):
    if times > 0:
        print(message)
        print_message(message, times - 1)

# Function call
print_message("Hello, Recursion!", 3)

Let's go step by step through how this recursive program works:

Condition Check: if times > 0, the function proceeds. In this case, times = 3, so the condition is true;
Print Message: the function prints "Hello, Recursion!";
Recursive Call: the function calls itself with times - 1;
Repetition: this process continues until times equals 0;
Termination: when the condition times > 0 is no longer true, the recursion stops, and the program completes.

Result: The message "Hello, Recursion!" is printed three times.

Task

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Given a string representing a phone number, which may contain spaces, dashes, parentheses, or other non-numeric characters. The goal is to extract only the digits using recursion.

If the input string number is empty, return an empty string.
Check if the first character of the string number is a digit using the isdigit() method in an if condition.
If it is a digit, concatenate it with the result of a recursive call to format_phone_number, passing the substring starting from the second character.
If it is not a digit, make a recursive call to format_phone_number, skipping the first character.

Solution

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Section 5. Chapter 1

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Recursion


              1234567
            
def print_message(message, times):
    if times > 0:
        print(message)
        print_message(message, times - 1)

# Function call
print_message("Hello, Recursion!", 3)

Let's go step by step through how this recursive program works:

Condition Check: if times > 0, the function proceeds. In this case, times = 3, so the condition is true;
Print Message: the function prints "Hello, Recursion!";
Recursive Call: the function calls itself with times - 1;
Repetition: this process continues until times equals 0;
Termination: when the condition times > 0 is no longer true, the recursion stops, and the program completes.

Result: The message "Hello, Recursion!" is printed three times.

Task

Swipe to start coding

If the input string number is empty, return an empty string.
Check if the first character of the string number is a digit using the isdigit() method in an if condition.
If it is a digit, concatenate it with the result of a recursive call to format_phone_number, passing the substring starting from the second character.
If it is not a digit, make a recursive call to format_phone_number, skipping the first character.

Solution

Switch to desktop for real-world practiceContinue from where you are using one of the options below

Everything was clear?

Thanks for your feedback!

Section 5. Chapter 1

Switch to desktop for real-world practiceContinue from where you are using one of the options below