datevid
diff --git a/‎strings/wave.py‎
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+def wave(txt: str) -> list:
+    """
+    Returns a so called 'wave' of a given string
+    >>> wave('cat')
+    ['Cat', 'cAt', 'caT']
+    >>> wave('one')
+    ['One', 'oNe', 'onE']
+    >>> wave('book')
+    ['Book', 'bOok', 'boOk', 'booK']
+    """
+
+    return [
+        txt[:a] + txt[a].upper() + txt[a + 1 :]
+        for a in range(len(txt))
+        if txt[a].isalpha()
+    ]
+
+
+if __name__ == "__main__":
+    __import__("doctest").testmod()