Lists and tuples#

Variables can also contain multiple entries of values. We call those lists and tuples. Some programmers also call them vectors or arrays; arrays of values. We already know one kind of array, strings. Strings are lists of characters.

See also

You can access elements in an array using square brackets [] which allow you access an element at a given index. Indexing starts at 0. Thus, the first element of an array is element number 0. The following string contains 5 characters and thus, element with index 0, 1, 2, 3 and 4 can be accessed:

word = "Hello"

word[0]

'H'

word[1]

'e'

word[2]

'l'

word[3]

'l'

word[4]

'o'

When accessing an index that is not in the list, we receive an error:

word[5]

---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
Input In [8], in <module>
----> 1 word[5]

IndexError: string index out of range

Numeric lists#

Another type of array are numeric lists. They are common to store measurements of experiments for example:

measurements = [5.5, 6.3, 7.2, 8.0, 8.8]

measurements[0]

5.5

measurements[1]

6.3

Changing entries in lists works like this:

measurements[1] = 25

measurements[1]

25

You can also append entries to lists:

measurements.append(10.2)

Lists can also be reversed:

measurements

[5.5, 25, 7.2, 8.0, 8.8, 10.2]

measurements.reverse()

measurements

[10.2, 8.8, 8.0, 7.2, 25, 5.5]

Just like strings, you can also concatenate arrays:

more_measurements = [12.3, 14.5, 28.3]

measurements + more_measurements

[10.2, 8.8, 8.0, 7.2, 25, 5.5, 12.3, 14.5, 28.3]

When working with numeric lists, you can use some of python’s built-in functions to do basic statistics on your measurements

# minimum value in the list
min(measurements)

5.5

# maximum value in the list
max(measurements)

25

# sum of all elements in the list
sum(measurements)

64.7

# number of elements in the list
len(measurements)

6

# average of all elements in the list
sum(measurements) / len(measurements)

10.783333333333333

Mixed type lists#

You can also store values of different types in a list

mixed_list = [22, 5.6, "Cat", 'Dog']

mixed_list[0]

22

mixed_list[3]

'Dog'

type(mixed_list[3])

str

Tuples#

Tuples are lists which cannot be changed:

immutable = (4, 3, 7.8)

immutable[1]

3

immutable[1] = 5

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Input In [31], in <module>
----> 1 immutable[1] = 5

TypeError: 'tuple' object does not support item assignment

You can convert tubles to lists and lists to tuples:

type(immutable)

tuple

mutable = list(immutable)

type(mutable)

list

again_immuntable = tuple(mutable)

type(again_immuntable)

tuple

Exercise#

Assume you did measurements on multiple days. Please compute average measurement of this week.

measurements_monday = [2.3, 3.1, 5.6]
measurements_tuesday = [1.8, 7.0]
measurements_wednesday = [4.5, 1.5, 6.4, 3.2]
measurements_thursday = [1.9, 2.0]
measurements_friday = [4.4]