Fix ruff (#12515)

* Empty commit

* Fix

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Fix

* Fix

* Fix

* updating DIRECTORY.md

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: MaximSmolskiy <MaximSmolskiy@users.noreply.github.com>

strings/wave_string.py

@@ -0,0 +1,20 @@
+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()