Assigning multiple values using tuple

[sivacg]

As a newbie, I am trying to understand the assigning multiple values using tuples. May I request one of you to help me here?

>>> a=('x','y','z')
>>> a
('x', 'y', 'z')
>>> a=(1,2,3)
>>> a
(1, 2, 3)
>>> a=(u,v,z)
Traceback (most recent call last):
  File "<pyshell#26>", line 1, in <module>
    a=(u,v,z)
NameError: name 'u' is not defined

2nd piece:

>>> a
(1, 2, 3)
>>> (u,v,z)=a
>>> u
1
>>> v
2
>>> z
3
>>> a
(1, 2, 3)

What is happening here exactly?

[Yoriz]

The statement

t = 12345, 54321, 'hello!'

is an example of tuple packing: the values 12345, 54321 and 'hello!' are packed together in a tuple. The reverse operation is also possible:

>>> x, y, z = t

This is called, appropriately enough, sequence unpacking and works for any sequence on the right-hand side. Sequence unpacking requires that there are as many variables on the left side of the equals sign as there are elements in the sequence. Note that multiple assignment is really just a combination of tuple packing and sequence unpacking.

[perfringo]

Despite the fact, that this is directly from documentation ("Sequence unpacking requires that there are as many variables on the left side of the equals sign as there are elements in the sequence.") one can have less variables than elements in sequence:

>>> start, *middle, end = (1, 2, 3, 4, 5)
>>> start
1
>>> middle
[2, 3, 4]
>>> end
5