Python tuples

1. Python tuples are just some values separated by commas:

   a_tuple = 123, 'abc', 456
   

2. A tuple can also be surrounded by parentheses

   a_tuple = (123, 'abc', 456)
   

3. Elements of a tuple can be accessed in the same way as with lists:

   >>> a_tuple[2]
   456
   

4. But, whereas lists are mutable (you can change one or more elements of a list), tuples are not. Compare:

   >>> a_tuple = 123, 'abc', 456
   >>> a_tuple
   (123, 'abc', 456)
   >>> a_tuple[2]
   456
   >>> a_tuple[2] = 789
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   TypeError: 'tuple' object does not support item assignment
   >>> a_list = [123, 'abc', 456]
   >>> a_list[2]
   456
   >>> a_list[2] = 789
   >>> a_list
   [123, 'abc', 789]
   >>>
   

5. You may put a trailing comma when writing a tuple:

   >>> b_tuple = 2,3,
   >>> b_tuple
   (2, 3)
   >>>
   

6. This comes in handy when writing a 1-tuple or singleton tuple which contains only one element.

   c = 2,
   

   If we had written it without a trailing comma, then it would represent the value of a number, not a tuple.

   Using parenteses doesn't help either, since they are used for grouping

   >>> d = (42)
   >>> d
   42
   >>> type(d)
   <type 'int'>
   

7. The 0-tuple is just written with parentheses

   e_tuple = ()