pytutorial/python_basics/tuple/README.md

Tuple

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The goal

Tuple are a non-mutable container which is typically used for heterogenic data types and is very important for functions with multiple return values.

Questions to David Rotermund

Tuples​

Tuples are immutable sequences, typically used to store collections of heterogeneous data (such as the 2-tuples produced by the enumerate() built-in). Tuples are also used for cases where an immutable sequence of homogeneous data is needed (such as allowing storage in a set or dict instance).

Examples

A tuple is a list of stuff that is enclosed in ( ) and seperated by , . An optional , after the last element is allowed.

a = (
    "a",
    "b",
    "c",
)
print(a)

a = ("a", "b", "c")
print(a)

Output:

('a', 'b', 'c')
('a', 'b', 'c')

Immutable

After creating a tuple cannot be modified. They are immutable.

a = (
    "a",
    "b",
    "c",
)

a[0] = "d" # -> TypeError: 'tuple' object does not support item assignment

But this doesn't mean that we can not stored mutable objects in a tuple. Furthermore these mutable objects stay mutable.

a = (
    ["a"],
    "b",
    "c",
)

a[0][0] = "d" # Okay, because changes the content of the list stored in a[0]
a[0] = "d" # -> TypeError: 'tuple' object does not support item assignment

Indexing

Idexing is the same as in lists.

a = (
    "a",
    2,
    3.3,
)

print(a[0]) # -> a
print(a[1]) # -> 2
print(a[-1]) # -> 3.3
print(a[:1]) # -> ('a',)
print(a[1:]) # -> (2, 3.3)
print(a[::2]) # -> ('a', 3.3)

*

a = (
    "a",
    2,
    3.3,
)

print(a*3)
print(3*a)

Output:

('a', 2, 3.3, 'a', 2, 3.3, 'a', 2, 3.3)
('a', 2, 3.3, 'a', 2, 3.3, 'a', 2, 3.3)

len()

a = (
    "a",
    2,
    3.3,
)

print(len(a)) # -> 3

+

a = (
    "a",
    2,
    3.3,
)

b = (
    "b",
    8.8,
    5,
)

print(a+b) # -> ('a', 2, 3.3, 'b', 8.8, 5)
print(b+a) # -> ('b', 8.8, 5, 'a', 2, 3.3)

in

a = (
    "a",
    2,
    3.3,
)


print(2 in a) # -> True
print(2 not in a) # -> False

index()

a = (
    "a",
    2,
    3.3,
)


print(a.index(2)) # -> 1 
print(a.index("a")) # -> 0

count()

a = (
    "a",
    2,
    3.3,
    "a",
    2,
    2,
)


print(a.count(2)) # -> 3
print(a.count("a")) # -> 2 

min() and max()

a = (
    9,
    2,
    3.3,
    22,
    2,
    2,
)

print(min(a)) # -> 2
print(max(a)) # -> 22

Strings are not allowed

a = (
    "a",
    2,
    3.3,
    "a",
    2,
    2,
)


print(min(a))
print(max(a))

Output:

TypeError: '<' not supported between instances of 'int' and 'str'

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​