primeiro commit com exercicios de Exercism realizados até esta data

python/isbn-verifier/isbn_verifier.py

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+def is_valid(isbn):
+    # remove dashes
+    isbn_no_dashes: str = "".join(isbn.split("-"))
+    sum: int = 0
+    # is isbn empty
+    if isbn == "":
+        return False
+    # isbn length must be 10
+    if len(isbn_no_dashes) < 10 or len(isbn_no_dashes) > 10:
+        return False
+    for index, digit in enumerate(isbn_no_dashes):
+        # non-digit in isbn not as a checksum, return False
+        if digit.isalpha() and index != 9:
+            return False
+        # if its a digit, ok
+        if digit.isdigit():
+            sum += int(digit) * (10 - index)
+        # if check digit is not digit or not an 'X', return False
+        if index == 9 and digit.isalpha() and digit.lower() != "x":
+            return False
+        # if check digit is the letter 'X' treat it as a 10
+        if digit.isalpha() and index == 9 and digit.lower() == "x":
+            sum += 10 * (10 - index)
+    return False if sum % 11 else True