How can I check if a string is a valid ISBN number in Python?
Ava W

To check if a string is a valid ISBN number in Python, you can use various approaches. The ISBN (International Standard Book Number) is a unique identifier assigned to books. Here's a long-form explanation of different methods to achieve this: 1. Regular Expression: - One approach is to use regular expressions to match and validate the format of the ISBN. - The ISBN can be either 10 digits (ISBN-10) or 13 digits (ISBN-13). - The patternr'^\d{9}[\d|X]$' matches a valid ISBN-10 number. - The patternr'^\d{13}$' matches a valid ISBN-13 number. - Use there.match() function to check if the string matches the appropriate pattern. - If it matches, returnTrue; otherwise, returnFalse. - Example:

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import re

def is_valid_isbn(isbn):
    pattern_isbn10 = r'^\d{9}[\d|X]$'
    pattern_isbn13 = r'^\d{13}$'
    
    if len(isbn) == 10:
   return bool(re.match(pattern_isbn10, isbn))
    elif len(isbn) == 13:
   return bool(re.match(pattern_isbn13, isbn))
    else:
   return False

2. Check Digit Calculation: - Another approach is to check the validity of the ISBN by calculating the check digit. - For ISBN-10, the last digit is the check digit, which is calculated based on the preceding 9 digits. - For ISBN-13, the check digit is calculated based on the preceding 12 digits. - Implement the algorithm to calculate the check digit and compare it with the last digit of the provided ISBN. - Example:

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def is_valid_isbn(isbn):
    isbn = isbn.replace("-", "").replace(" ", "")  # Remove hyphens and spaces
    
    if len(isbn) == 10:
   if not isbn[:-1].isdigit():
  return False
   
   check_digit = 0 if isbn[-1].upper() == "X" else int(isbn[-1])
   digits = [int(char) for char in isbn[:-1]]
   calculated_check_digit = sum((i + 1) * digit for i, digit in enumerate(digits)) % 11
   
   return calculated_check_digit == check_digit
    
    elif len(isbn) == 13:
   if not isbn.isdigit():
  return False
   
   check_digit = int(isbn[-1])
   digits = [int(char) for char in isbn[:-1]]
   calculated_check_digit = (10 - sum((3 if i % 2 == 0 else 1) * digit for i, digit in enumerate(digits))) % 10
   
   return calculated_check_digit == check_digit
    
    else:
   return False

3. External Libraries: - You can also utilize external libraries such asisbnlib to validate ISBN numbers. - Install theisbnlib library using pip:pip install isbnlib. - Use theisbnlib.is_isbn() function to check if the provided string is a valid ISBN. - Example:

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import isbnlib

def is_valid_isbn(isbn):
    return isbnlib.is_isbn(isbn)

Choose the method that best suits your requirements. Regular expressions provide flexibility and control over the ISBN format, while check digit calculation offers a more custom approach. Utilizing external libraries can provide convenience and handle more complex ISBN validation scenarios.

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