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Tuple
{:.no_toc}
* TOC {:toc}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 |