Python: isbn_verifier

python/isbn-verifier/isbn_verifier.py

@@ -0,0 +1,29 @@
+ISBN_LENGTH = 10
+
+
+def is_valid(isbn):
+
+    isbn = isbn.replace('-', '')
+    if len(isbn) != ISBN_LENGTH:
+        return False
+
+    checksum = 0
+
+    for ch, i in zip(isbn, range(ISBN_LENGTH, 1, -1)):
+        if not ch.isdigit():
+            return False
+
+        checksum += int(ch)*i
+
+    ch = isbn[-1]
+
+    if ch.isdigit():
+        x = int(ch)
+    elif ch == 'X':
+        x = 10
+    else:
+        return False
+
+    checksum += x
+
+    return checksum % 11 == 0