Sequence

Sequence is a generic term for an ordered collection of things. Basic sequence types include:

• string
• list
• tuple
• range

Most sequence types in Python support the following basic sequence operations:

Access via index

Get element by its position (index). Indexes start with 0.

s[n] # access nth element of s

Examples:

"Geronimo"[0]  # "G"
"Geronimo"[3]  # "o"

[1, 2, 3][0]   # 1
[1, 2, 3][2]   # 3

Length

Length is another word for size. Lengths start with 1, unlike indexes.

len(s)  # length of s

Examples:

len("Geronimo") # 8
len("Ge")       # 2

len([])         # 0
len([1, 2, 3])  # 3

min and max

Returns minimum and maximum value from a sequence. When items are characters, lexicographic order is used.

min(s)
max(s)

Examples:

min([1, 2, 3])  # 1
max([1, 2, 3])  # 3

min("azbc")  # 'a'
max("azbc")  # 'z'

Count method

Returns the total number of occurrences of an element in a sequence.

s.count(x)  ## number of occurrences of x in s

Examples:

"Freedom".count("e")  # 2
"Freedom".count("r")  # 1

[1, 1, 6, 8, 8, 8].count(1)  # 2
[1, 1, 6, 8, 8, 8].count(8)  # 3

in and not in

Determines if a sequence includes and element or doesn't include it.

x in s     # True if s contains x
x not in s # True if s doesn't contain x

Examples:

word = "France"
"o" in word  # True
"z" in word  # False

"z" not in word # True
"F" not in word # False

Concatenation

Glues together two sequences.

x + y

Examples:

name = "Peter"
city = "Oslo"
result = name + city # "PeterOslo"

a = [1, 2, 3]
b = [4, 5, 6]
c = a + b # [1, 2, 3, 3, 4, 5]

Slicing

Produces a subsequence.

s[a:b] # get subsequence of s from a to b
s[:b]  # get subsequence of s from 0 to b
s[a:]  # get subsequence of s from a to end
s[:]   # get subsequence of s from 0 to end
       # (esssentially, full copy of s)

Examples:

"France"[1:3]   # "ra"
"France"[2:5]   # "anc"

[0, 1, 2, 3, 4][1:3]   # [1, 2]
[0, 1, 2, 3, 4][2:5]   # [2, 3, 4]

"France"[:3]   # "Fra"
"France"[2:]   # "ance"
"France"[:]   # "France"

Multiplication

Produces a repeated sequence.

s * n  # make n copies of s

"A" * 4    # "AAAA"
"Joe" * 2  # "JoeJoe"

[1,2,3] * 3  # [1, 2, 3, 1, 2, 3, 1, 2, 3]

Unpacking

To unpack a sequence is to assign all the sequence entries to multiple variables in a single operation.

Example, unpacking a tuple:

date = (2019,9,10)
year, month, day = date
print(year)
print(month)
print(day)

2019
9
10