Merge pull request #126 from ikostan/main

Update from master

Author: ikostan

solutions/python/isbn-verifier/6/isbn_verifier.py

@@ -0,0 +1,43 @@
+"""
+ISBN Verifier.
+
+The ISBN-10 verification process is used to validate book identification
+numbers. These normally contain dashes and look like: 3-598-21508-8
+
+ISBN
+The ISBN-10 format is 9 digits (0 to 9) plus one check character
+(either a digit or an X only). In the case the check character is an X,
+this represents the value '10'. These may be communicated with or without
+hyphens, and can be checked for their validity by the following formula:
+
+(d₁ * 10 + d₂ * 9 + d₃ * 8 + d₄ * 7 + d₅ * 6 +
+d₆ * 5 + d₇ * 4 + d₈ * 3 + d₉ * 2 + d₁₀ * 1) mod 11 == 0
+
+If the result is 0, then it is a valid ISBN-10, otherwise it is invalid.
+"""
+
+
+def is_valid(isbn: str) -> bool:
+    """
+    Verify ISBN.
+
+    :param isbn: 9 digits ISBN 10 format
+    :return: Tru if isbn is valid, False otherwise
+    """
+    isbn_digits: list[int] = []
+    for char in isbn:
+        if char == "-":
+            continue
+        elif char.isdigit():
+            isbn_digits.append(int(char))
+        elif char.upper() == "X" and len(isbn_digits) == 9:
+            isbn_digits.append(10)
+        else:
+            return False
+    # ISBN total length should be = 10
+    if len(isbn_digits) != 10:
+        return False
+
+    return (
+        sum(digit * (10 - i) for i, digit in enumerate(isbn_digits)) % 11 == 0
+    )