241 lines
3.6 KiB
Markdown
241 lines
3.6 KiB
Markdown
# Tuple
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{:.no_toc}
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<nav markdown="1" class="toc-class">
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* TOC
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{:toc}
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</nav>
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## The goal
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Tuple are a non-mutable container which is typically used for heterogenic data types and is very important for functions with multiple return values.
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Questions to [David Rotermund](mailto:davrot@uni-bremen.de)
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## [Tuples](https://docs.python.org/3/library/stdtypes.html#tuple)
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> 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).
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# Examples
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A tuple is a list of stuff that is enclosed in **( )** and seperated by **,** . An optional **,** after the last element is allowed.
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```python
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a = (
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"a",
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"b",
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"c",
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)
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print(a)
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a = ("a", "b", "c")
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print(a)
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```
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Output:
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```python
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('a', 'b', 'c')
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('a', 'b', 'c')
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```
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## Immutable
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After creating a tuple cannot be modified. They are immutable.
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```python
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a = (
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"a",
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"b",
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"c",
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)
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a[0] = "d" # -> TypeError: 'tuple' object does not support item assignment
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```
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But this doesn't mean that we can not stored mutable objects in a tuple. Furthermore these mutable objects stay mutable.
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```python
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a = (
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["a"],
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"b",
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"c",
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)
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a[0][0] = "d" # Okay, because changes the content of the list stored in a[0]
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a[0] = "d" # -> TypeError: 'tuple' object does not support item assignment
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```
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## Indexing
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Idexing is the same as in lists.
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```python
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a = (
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"a",
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2,
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3.3,
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)
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print(a[0]) # -> a
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print(a[1]) # -> 2
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print(a[-1]) # -> 3.3
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print(a[:1]) # -> ('a',)
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print(a[1:]) # -> (2, 3.3)
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print(a[::2]) # -> ('a', 3.3)
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```
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## *
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```python
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a = (
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"a",
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2,
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3.3,
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)
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print(a*3)
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print(3*a)
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```
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Output:
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```python
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('a', 2, 3.3, 'a', 2, 3.3, 'a', 2, 3.3)
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('a', 2, 3.3, 'a', 2, 3.3, 'a', 2, 3.3)
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```
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## len()
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```python
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a = (
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"a",
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2,
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3.3,
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)
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print(len(a)) # -> 3
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```
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## +
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```python
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a = (
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"a",
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2,
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3.3,
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)
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b = (
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"b",
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8.8,
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5,
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)
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print(a+b) # -> ('a', 2, 3.3, 'b', 8.8, 5)
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print(b+a) # -> ('b', 8.8, 5, 'a', 2, 3.3)
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```
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## in
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```python
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a = (
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"a",
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2,
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3.3,
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)
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print(2 in a) # -> True
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print(2 not in a) # -> False
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```
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## index()
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```python
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a = (
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"a",
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2,
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3.3,
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)
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print(a.index(2)) # -> 1
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print(a.index("a")) # -> 0
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```
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## count()
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```python
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a = (
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"a",
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2,
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3.3,
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"a",
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2,
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2,
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)
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print(a.count(2)) # -> 3
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print(a.count("a")) # -> 2
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```
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## min() and max()
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```python
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a = (
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9,
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2,
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3.3,
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22,
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2,
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2,
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)
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print(min(a)) # -> 2
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print(max(a)) # -> 22
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```
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Strings are not allowed
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```python
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a = (
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"a",
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2,
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3.3,
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"a",
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2,
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2,
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)
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print(min(a))
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print(max(a))
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```
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Output:
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```python
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TypeError: '<' not supported between instances of 'int' and 'str'
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```
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## [Common Sequence Operations](https://docs.python.org/3/library/stdtypes.html#sequence-types-list-tuple-range)
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|Operation|Result|
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|x in s|True if an item of s is equal to x, else False|
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|x not in s|False if an item of s is equal to x, else True|
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|s + t|the concatenation of s and t|
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|s * n or n * s|equivalent to adding s to itself n times|
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|s[i]|ith item of s, origin 0|
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|s[i:j]|slice of s from i to j|
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|s[i:j:k]|slice of s from i to j with step k|
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|len(s)|length of s|
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|min(s)|smallest item of s|
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|max(s)|largest item of s|
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|s.index(x[, i[, j]])|index of the first occurrence of x in s (at or after index i and before index j)|
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|s.count(x)|total number of occurrences of x in s|
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