Sequence Types: list

The goal

Lists are mutable sequences, typically used to store collections of homogeneous items (where the precise degree of similarity will vary by application).

Quote

Questions to David Rotermund

Example Lists

With homogeneous items:

primes = [2, 3, 5, 7]

collection_of_strings = [
    "AA",
    "BB",
    "CC",
    "DD",
    "EE",
    "FF",
    "GG",
    "HH",
]

A mixture of type:

def my_function(a):
    return a

my_favourite_things = [32, "sleep", my_function]

Indexing

collection_of_strings = [
    "AA",
    "BB",
    "CC",
    "DD",
    "EE",
    "FF",
    "GG",
    "HH",
]


print(collection_of_strings[0])  # -> AA
print(collection_of_strings[1])  # -> BB
print(collection_of_strings[-2])  # -> GG
print(collection_of_strings[-1])  # -> HH

Slicing

collection_of_strings = [
    "AA",
    "BB",
    "CC",
    "DD",
    "EE",
    "FF",
    "GG",
    "HH",
]


print(collection_of_strings[0:3])  # -> ['AA', 'BB', 'CC']
print(collection_of_strings[:3])  # -> ['AA', 'BB', 'CC']
print(collection_of_strings[3:])  # -> ['DD', 'EE', 'FF', 'GG', 'HH']
print(collection_of_strings[1:-1])  # -> ['BB', 'CC', 'DD', 'EE', 'FF', 'GG']
print(collection_of_strings[-3:])  # -> ['FF', 'GG', 'HH']
print(collection_of_strings[0:3])  # -> ['AA', 'BB', 'CC']
print(collection_of_strings[0:3:1])  # -> ['AA', 'BB', 'CC']
print(collection_of_strings[0:3:2])  # -> ['AA', 'CC']
print(collection_of_strings[::2])  # -> ['AA', 'CC', 'EE', 'GG']

Changing lists

collection_of_strings = [
    "AA",
    "BB",
    "CC",
    "DD",
    "EE",
    "FF",
    "GG",
    "HH",
]

collection_of_strings[3] = "II"
print(collection_of_strings)  # -> ['AA', 'BB', 'CC', 'II', 'EE', 'FF', 'GG', 'HH']
collection_of_strings[:3] = ["JJ", "KK", "LL"]
print(collection_of_strings)  # -> ['JJ', 'KK', 'LL', 'II', 'EE', 'FF', 'GG', 'HH']
collection_of_strings[:4] = [
    "MM",
    "NN",
    "OO",
    "PP",
]
print(collection_of_strings)  # -> ['MM', 'NN', 'OO', 'PP', 'EE', 'FF', 'GG', 'HH']

List functions

len() and sorted()

collection_of_strings = [
    "GG",
    "HH",
    "AA",
    "BB",
    "EE",
    "FF",
    "CC",
    "DD",
]


print(len(collection_of_strings))  # -> 8
print(sorted(collection_of_strings)) # -> ['AA', 'BB', 'CC', 'DD', 'EE', 'FF', 'GG', 'HH']

max(), min and sum()

primes = [2, 3, 5, 7]
print(sum(primes)) # -> 17
print(max(primes)) # -> 7
print(min(primes)) # -> 2

in

Is x in list?

collection_of_strings = [
    "AA",
    "BB",
    "CC",
    "DD",
    "EE",
    "FF",
    "GG",
    "HH",
]
print("AA" in collection_of_strings) # -> True
print("XX" in collection_of_strings) # -> False
print("AA" not in collection_of_strings) # -> False
print("XX" not in collection_of_strings) # -> True

Index

Which index id has an element in a list?

collection_of_strings = [
    "AA",
    "BB",
    "CC",
    "DD",
    "EE",
    "FF",
    "GG",
    "HH",
]

print(collection_of_strings.index("CC"))  # -> 2
print(collection_of_strings.index("XX"))  # -> ValueError: 'XX' is not in list

Maybe we don’t want to start in the beginning of the list or don’t want to search until the end of the list:

collection_of_strings = [
    "AA",
    "BB",
    "CC",
    "DD",
    "EE",
    "BB",
    "FF",
    "GG",
    "BB",
    "HH",
]
print(collection_of_strings.index("BB"))  # -> 1
# At or after 2
print(collection_of_strings.index("BB", 2))  # -> 5
# Before 6
print(collection_of_strings.index("BB", 2, 6)) # -> 5
# Before 4
print(collection_of_strings.index("BB", 2, 4))  # ValueError: 'BB' is not in list

append(), pop(), and remove()

collection_of_strings = [
    "AA",
    "BB",
    "BB",
    "CC",
    "DD",
    "EE",
    "FF",
    "GG",
    "HH",
]

collection_of_strings.append("II")
print(
    collection_of_strings
)  # -> ['AA', 'BB', 'BB', 'CC', 'DD', 'EE', 'FF', 'GG', 'HH', 'II']
print(collection_of_strings.pop())  # -> II
print(
    collection_of_strings
)  # -> ['AA', 'BB', 'BB', 'CC', 'DD', 'EE', 'FF', 'GG', 'HH']

collection_of_strings.remove("BB")
print(collection_of_strings)  # -> ['AA', 'BB', 'CC', 'DD', 'EE', 'FF', 'GG', 'HH']

collection_of_strings.remove("BB")
print(collection_of_strings)  # -> ['AA', 'BB', 'CC', 'DD', 'EE', 'FF', 'GG', 'HH']

collection_of_strings.remove("BB")
print(collection_of_strings)  # -> ValueError: list.remove(x): x not in list

del and insert()

Insert and delete an element.

collection_of_strings = []
collection_of_strings.append("BB")
collection_of_strings.append("CC")
collection_of_strings.append("DD")
print(collection_of_strings)  # -> ['BB', 'CC', 'DD']

collection_of_strings.insert(0, "AA")
print(collection_of_strings)  # -> ['AA', 'BB', 'CC', 'DD']

del collection_of_strings[1]
print(collection_of_strings)  # -> ['AA', 'CC', 'DD']

+

Concatenating lists.

collection_of_strings_a = [
    "AA",
    "BB",
    "CC",
    "DD",
]
collection_of_strings_b = [
    "EE",
    "FF",
    "GG",
    "HH",
]
print(collection_of_strings_a)  # -> ['AA', 'BB', 'CC', 'DD']
print(collection_of_strings_b)  # -> ['EE', 'FF', 'GG', 'HH']
collection_of_strings = collection_of_strings_a + collection_of_strings_b

print(collection_of_strings)  # -> ['AA', 'BB', 'CC', 'DD', 'EE', 'FF', 'GG', 'HH']

*

Repeat a list several times.

collection_of_strings = [
    "AA",
    "BB",
    "CC",
]
print(3 * collection_of_strings) # -> ['AA', 'BB', 'CC', 'AA', 'BB', 'CC', 'AA', 'BB', 'CC']
print(collection_of_strings * 3) # -> ['AA', 'BB', 'CC', 'AA', 'BB', 'CC', 'AA', 'BB', 'CC']

count()

How often does an element occur in the list?

collection_of_strings = [
    "AA",
    "AA",
    "BB",
    "BB",
    "BB",
    "CC",
    "DD",
    "EE",
    "FF",
    "GG",
    "HH",
]
print(collection_of_strings.count("AA"))  # -> 2
print(collection_of_strings.count("BB"))  # -> 3
print(collection_of_strings.count("CC"))  # -> 1

Additional commands


list.append(x)
list.extend(iterable)
list.insert(i, x)
list.remove(x)
list.pop([i])
list.clear()
list.index(x[, start[, end]])
list.count(x)
list.sort(*, key=None, reverse=False)
list.reverse()
list.copy()

Common Sequence Operations

Operation	Result
x in s	True if an item of s is equal to x, else False
x not in s	False if an item of s is equal to x, else True
s + t	the concatenation of s and t
s * n or n * s	equivalent to adding s to itself n times
s[i]	ith item of s, origin 0
s[i:j]	slice of s from i to j
s[i:j:k]	slice of s from i to j with step k
len(s)	length of s
min(s)	smallest item of s
max(s)	largest item of s
s.index(x[, i[, j]])	index of the first occurrence of x in s (at or after index i and before index j)
s.count(x)	total number of occurrences of x in s

The source code is Open Source and can be found on GitHub.