[Sync Iteration] python/diamond/1

solutions/python/diamond/1/diamond.py

@@ -0,0 +1,39 @@
+"""
+The diamond kata takes as its input a letter, and outputs it in
+a diamond shape. Given a letter, it prints a diamond starting
+with 'A', with the supplied letter at the widest point.
+"""
+
+import string
+
+CHARS: str = string.ascii_uppercase
+
+
+def rows(letter: str) -> list:
+    """
+    Return the diamond rows from 'A' to ``letter``.
+
+    Builds the upper half and mirrors it to form a symmetric diamond.
+
+    :param str letter: Uppercase letter (``'A'``-``'Z'``) marking the widest row.
+    :returns: The full diamond as a list of strings, one per row.
+    :rtype: list
+    :raises ValueError: If ``letter`` is not an ASCII uppercase character.
+    """
+    result: list = []
+    letter_index: int = CHARS.index(letter)
+    row_length: int = (letter_index * 2) + 1
+
+    for i, char in enumerate(CHARS[: letter_index + 1]):
+        # All rows have as many trailing spaces as leading spaces.
+        spaces: str = " " * (letter_index - i)
+        # The first/last row contains one 'A'.
+        if i == 0:
+            result.append(spaces + char + spaces)
+        else:
+            middle: str = " " * (row_length - 2 - (len(spaces) * 2))
+            # All rows, except the first and last, have exactly two identical letters.
+            result.append(spaces + char + middle + char + spaces)
+    # Mirror the list: the bottom half has the letters in descending order.
+    result = result + result[::-1][1:]
+    return result