04. Special sequences ranges, tuples and lists

We've already covered strings, and learned about `bytes` and `bytesarrays` in the previous lesson. Now let's dive into the more interesting sequences - ranges, tuples and lists.

1) Ranges

Ranges are a list of integers, usually in a consecutive order. They are most commonly used to initiate and feed values within loops.

Creating a range

There are several options for declaring a range.

`range(n)`
`0` up to but not including `m`.
`range(m,n)`
`m` up to but not including `n`.
`range(m, n, step)`
`m` up to but not including `n` with increments step.

2) Tuples

Tuples are immutable sequences that can contain any type of element.

Declaring tuples

Tuples are declared with parentheses (`()`). We can have a one-element tuples such as `test,)` or an empty tuple `()`. The comma for one-element tuples is necessary since the parentheses can be interpreted as a mathematical notation.

A simple example of a tuple is the a pair of numbers describing the xy-coordinate system.

given a sequence as an argument, tuple function creates a tuple containing the elements of the sequence

``````>>> tuple('banana')
('b', 'a', 'n', 'a', 'n', 'a')
>>> tuple(range(2, 10, 2))
(2, 4, 6, 8)``````

Tuple packing in functions

Since functions may return only one value, it's useful to use tuples when we want to return two or more datasets.

``````>>> def doubleTwoNumbers(x,y):
...    return (2*x, 2*y)
>>> print(doubleTwoNumbers(4,5))
(8, 10)``````

Exchanging tuples

You can easily exchange tuples with `left, right = right, let`. Let's see how we can use tuples to write out the fibonacci sequence.

``````>>> def fib(n):
...    a,b = 1,1
...    for i in range(n-1):
...        a,b = b,a+b
...    return a
>>> fib(5)
5``````

3) Lists

Lists are a comma-separated series of mutable values of any type of element. They're like a tuples, but better, with added flexibility.

Lists may contain items of different data types, but usually, they're all of the same type.

Declaring a list

Lists are declared between square brackets (`[]`).

``````>>> fruits = ['apple', 'banana', 'pineapple']
>>> print(fruits)
['apple', 'banana', 'pineapple']
>>> min(fruits)
'apple'
>>> 'pineapple' in fruits
True
>>> vegetables = ['kale', 'carrot', 'lettuce']
>>> vegetables + fruits
['kale', 'carrot', 'lettuce', 'apple', 'banana', 'pineapple']``````

As you can see, you can apply any sequence functions to our lists.

Nesting lists

You may also nest lists to create lists within lists.

``````>>> nested = [['a', 'b', 'c'], 'c']
>>> nested[0]
['a', 'b', 'c']
>>> nested[1]
'c'``````

Lists modifications

One unique property of lists is that they are mutable. This means you can change a variable from within the list. Take a look here of the list `l` and min/max indices `i` and `j`.

`l[i] = x`
Replace value at index `i` with value `x`.
`l[i:j] = coll`
Replace value from `i` up to but not including `j` with `coll`.
`l[i:j] = []`
Delete values stored from `i` up to but not including `j`.
`l[i:j:k] = coll`
Replace incrementally with step size `k`.
`l[n:n] = coll`
Insert elements of `coll` before the nth element of the list.
`l[:] = coll`
Replace entire contents of list `l` with `coll`.

Delete statement

Another way to remove list items is with the `del` keyword.

`del lst[n]`
Remove the `n`th element from lst.
`del lst[i:j]`
Remove elements from `i` through but not including `j`.
`del lst[i:j:k]`
Remove every `k`th element from `i` up to but not including `j`.

List modifications

`l.extend(L)`
Extend the list by appending with collection `L`.
`l.insert(i, x)`
Inserts `x` before the `i`th element of `l`.
`l.remove(x)`
Remove the first occurrence of `x`.
If `x` does not exist, an error comes up.
`l.append(x)`
Append `x` to the end of `l`.
`l.pop([i])`
Remove the `i`th element and return it.
`l.reverse()`
Reverses the list.
`l.sort()`
Sort the list `l`.

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