list_example = [1, 2, 3, 4, 55, 6, 6]
tuple_example = (1, 2, 3, 4, 55, 6, 6)
set_example = {1, 2, 3, 4, 55, 6, 6}
dictionary_example = {1: "One", 2: "Two", 3: "Three", 4: "Four", 5: "Five"}

print(len(list_example), "-> ", list_example)
print(len(tuple_example), "-> ", tuple_example)
print(len(set_example), "-> ", set_example)
print(len(dictionary_example), "-> ", dictionary_example)

Output:

7 :  [1, 2, 3, 4, 55, 6, 6]
7 :  (1, 2, 3, 4, 55, 6, 6)
6 :  {1, 2, 3, 4, 6, 55}  : order of elements is not preserved and duplicates are not allowed in sets.

Lists are defined by a pair of [],

• The elements of a list can be modified in the runtime
• The elements are accessed by an index number
• The same item can be added as many times as necessary, at different positions in the list
• The insertion order of elements is preserved until the list is modified

Tuples are defined by a pair of (),

• The elements of a tuple cannot be modified in the runtime
• The elements are accessed by an index number
• The same item can be added as many times as necessary, at different positions in the tuple
• The insertion order of elements is preserved throughout the life span of the tuple

Sets are defined by a pair of {},

• The elements stored in a set have to be unique, no matter how many times they are added to the set, duplicates are not allowed.
• The order of elements is not guaranteed to be preserved as the order of insertion to the set

Dictionaries are also defined by a pair of {},

• Dictionaries are special type of sets where the keys are unique as in sets
• The ordering is similar to the sets based on the keys
• len() of a dictionary is the number of keys in the dictionary

The positional order does not imply the incremental or decremental ordering based on magnitude of numbers or the lexicographic ordering of strings in a list or a tuple. If such an ordering is necessary, the programmers will need to sort the items in the list or the tuple.