Unpacking a Sequence into Separate Variables

Problem

• You have an N-element tuple or sequence that you would like to unpack into a collection of N variables.

Solution

Any sequence (or iterable) can be unpacked into variables using a simple assignment operation. The only requirement is that the number of variables and structure match the sequence.

Example 1

# Example 1
p = (4, 5)
x, y = p
print x
print y

4
5

Example 2

# Example 2
data = ['ACME', 50, 91.1, (2012, 12, 21)]
name, shares, price, date = data
print name
print date

name, shares, price, (year, mon, day) = data
print name
print year
print mon
print day

ACME
(2012, 12, 21)
ACME
2012
12
21

Example 3

• If there is a mismatch in the number of elements, you’ll get an error

# Example 3
# error with mismatch in number of elements
p = (4, 5)
x, y, z = p

---------------------------------------------------------------------------

ValueError                                Traceback (most recent call last)

<ipython-input-3-b612f455712e> in <module>()
      2 # error with mismatch in number of elements
      3 p = (4, 5)
----> 4 x, y, z = p


ValueError: need more than 2 values to unpack

Example 4

• Unpacking actually works with any object that happens to be iterable, not just tuples or lists. This includes strings, files, iterators, and generators.

# Example 4: string
s = 'Hello'
a, b, c, d, e = s
print a
print b
print e

H
e
o

Example 5

• Discard certain values

# Example 5
# discard certain values
data = [ 'ACME', 50, 91.1, (2012, 12, 21) ]
_, shares, price, _ = data
print shares
print price

50
91.1