Create join.py (#5363)

* Create join.py

Because we have a split.py

* Update join.py

* Update join.py

* Update join.py

* Update join.py

* Update join.py

* Update strings/join.py

Co-authored-by: John Law <johnlaw.po@gmail.com>

* Update join.py

* Update join.py

* Update join.py

* Update join.py

Co-authored-by: John Law <johnlaw.po@gmail.com>

strings/join.py

@@ -0,0 +1,32 @@
+"""
+Program to join a list of strings with a given separator
+"""
+
+
+def join(separator: str, separated: list) -> str:
+    """
+    >>> join("", ["a", "b", "c", "d"])
+    'abcd'
+    >>> join("#", ["a", "b", "c", "d"])
+    'a#b#c#d'
+    >>> join("#", "a")
+    'a'
+    >>> join(" ", ["You", "are", "amazing!"])
+    'You are amazing!'
+    >>> join("#", ["a", "b", "c", 1])
+    Traceback (most recent call last):
+    ...
+    Exception: join() accepts only strings to be joined
+    """
+    joined = ""
+    for word_or_phrase in separated:
+        if not isinstance(word_or_phrase, str):
+            raise Exception("join() accepts only strings to be joined")
+        joined += word_or_phrase + separator
+    return joined.strip(separator)
+
+
+if "__name__" == "__main__":
+    from doctest import testmod
+
+    testmod()