Packing and Unpacking Tuples

Tuples in Python are values separated by commas. Enclosing parentheses for inputting tuples are optional, so the two assignments

a = 1, 2, 3   # a is the tuple (1, 2, 3)

and

a = (1, 2, 3) # a is the tuple (1, 2, 3)

are equivalent. The assignment a = 1, 2, 3 is also called packing because it packs values together in a tuple.

Note that a one-value tuple is also a tuple. To tell Python that a variable is a tuple and not a single value you can use a trailing comma

a = 1  # a is the value 1
a = 1, # a is the tuple (1,)

A comma is needed also if you use parentheses

a = (1,) # a is the tuple (1,)
a = (1)  # a is the value 1 and not a tuple

To unpack values from a tuple and do multiple assignments use

# unpacking AKA multiple assignment
x, y, z = (1, 2, 3) 
# x == 1
# y == 2
# z == 3

The symbol \_ can be used as a disposable variable name if one only needs some elements of a tuple, acting as a placeholder:

a = 1, 2, 3, 4
_, x, y, _ = a
# x == 2
# y == 3

Single element tuples:

x, = 1,  # x is the value 1
x  = 1,  # x is the tuple (1,)

In Python 3 a target variable with a \* prefix can be used as a catch-all variable (see http://stackoverflow.com/documentation/python/809/compatibility-between-python-3-and-python-2/2845/unpacking-iterables ):

first, *more, last = (1, 2, 3, 4, 5)
# first == 1
# more == [2, 3, 4]
# last == 5