====== collections ======

  * **List** ''[ "abc", 1, True ]''
    * ordered, indexed, allow duplicate items
    * mutable
    * list item can be any type
  * **Tuple** ''( 1, "A", True)''
    * ordered, indexed, allow duplicate items
    * **immutable**
    * tuple item can be any type
  * **Set** ''{ "abc", 34, True }''
    * **unordered**, unindexed, no duplicate items
      * ''1'' and ''True'' (and ''0/False'') are the same items (duplicates)
    * items are immutable
    * set is mutable (add/remove items)
    * set item can be any type
  * **Dictionary** ''{ "keyA": value, "keyB": value }''
    * stores ''key:value'' pairs
    * ordered (from v3.7), no duplicate items (keys)
    * mutable
    * value can be any type