list是一種可變的集合，其中的項目按_順序_排列。就像大多數集合一樣（參見內建的 tuple、dict 和 set），陣列可以參照任何（或多種）資料型態，包括其他陣列。如同任何序列，可以透過從左邊算起的 0-based index 編號，或從右邊算起的 -1-based index 來存取項目。陣列可以透過切片表示法或<list>.copy()來整份或部分複製。
陣列同時支援一般和可變序列操作，例如min()/max()、<list>.index()、<list>.append()和<list>.reverse()。陣列元素可以使用for item in <list>建構來疊代。當同時需要元素索引和元素值時，可以使用for index, item in enumerate(<list>)。
在底層，lists是以動態陣列實作的，類似 Java 的ArrayList型別，最常用來儲存長度未知、性質相近的一組資料（字串、數字、集合等）。陣列是非常有彈性又實用的資料結構，Python 中許多內建方法和操作都會產生陣列作為輸出。
建構
list可以用_字面值_來宣告，兩側是方括號[]，並以逗號分隔元素：
>>> no_elements = []
>>> no_elements
[]
>>> one_element = ["Guava"]
>>> one_element
['Guava']
>>> elements_separated_with_commas = ["Parrot", "Bird", 334782]
>>> elements_separated_with_commas
['Parrot', 'Bird', 334782]
為了方便閱讀，當list中有許多元素或巢狀資料結構時，可以加上換行：
>>> lots_of_entries = [
"Rose",
"Sunflower",
"Poppy",
"Pansy",
"Tulip",
"Fuchsia",
"Cyclamen",
"Lavender"
]
>>> lots_of_entries
['Rose', 'Sunflower', 'Poppy', 'Pansy', 'Tulip', 'Fuchsia', 'Cyclamen', 'Lavender']
# Each data structure is on its own line to help clarify what they are.
>>> nested_data_structures = [
{"fish": "gold", "monkey": "brown", "parrot": "grey"},
("fish", "mammal", "bird"),
['water', 'jungle', 'sky']
]
>>> nested_data_structures
[{'fish': 'gold', 'monkey': 'brown', 'parrot': 'grey'}, ('fish', 'mammal', 'bird'), ['water', 'jungle', 'sky']]
list()建構子可以空著使用，也可以接受一個_可疊代物件_作為引數。建構子會依序走訪可疊代物件中的每個元素，並將它們加入list：
>>> no_elements = list()
>>> no_elements
[]
# The tuple is unpacked and each element is added.
>>> multiple_elements_from_tuple = list(("Parrot", "Bird", 334782))
>>> multiple_elements_from_tuple
['Parrot', 'Bird', 334782]
# The set is unpacked and each element is added.
>>> multiple_elements_from_set = list({2, 3, 5, 7, 11})
>>> multiple_elements_from_set
[2, 3, 5, 7, 11]
用list建構子搭配string或dict時，結果可能會出乎意料：
# String elements (Unicode code points) are iterated through and added *individually*.
>>> multiple_elements_string = list("Timbuktu")
>>> multiple_elements_string
['T', 'i', 'm', 'b', 'u', 'k', 't', 'u']
# Unicode separators and positioning code points are also added *individually*.
>>> multiple_code_points_string = list('अभ्यास')
>>> multiple_code_points_string
['अ', 'भ', '्', 'य', 'ा', 'स']
# The iteration default for dictionaries is over the keys, so only key data is inserted into the list.
>>> source_data = {"fish": "gold", "monkey": "brown"}
>>> multiple_elements_dict_1 = list(source_data)
['fish', 'monkey']
由於list建構子只接受_可疊代物件_（或什麼都不接受）作為引數，_不可_疊代的物件會擲回型別錯誤。因此，改用字面值的方式來建立只有一個項目的list，會簡單得多。
# Numbers are not iterable, and so attempting to create a list with a number passed to the constructor fails.
>>> one_element = list(16)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'int' object is not iterable
# Tuples *are* iterable, so passing a one-element tuple to the constructor does work, but it's awkward
>>> one_element_from_iterable = list((16,))
>>> one_element_from_iterable
[16]
存取元素
陣列中的項目（以及其他序列型別str和tuple中的項目）可以透過0-based index和_括號表示法_來存取。索引可以從**left到right（從零開始），也可以從right到left**（從 -1 開始）。
從左側算起的索引 ⟹
|
0
👇🏾 |
1
👇🏾 |
2
👇🏾 |
3
👇🏾 |
4
👇🏾 |
5
👇🏾 |
| P |
y |
t |
h |
o |
n |
👆🏾
-6 |
👆🏾
-5 |
👆🏾
-4 |
👆🏾
-3 |
👆🏾
-2 |
👆🏾
-1 |
|
⟸ 從右側算起的索引 |
>>> breakfast_foods = ["Oatmeal", "Fruit Salad", "Eggs", "Toast"]
# Oatmeal is at index 0 or index -4.
>>> breakfast_foods[0]
'Oatmeal'
>>> breakfast_foods[-4]
'Oatmeal'
# Eggs are at index -2 or 2
>>> breakfast_foods[-2]
'Eggs'
>>> breakfast_foods[2]
'Eggs'
# Toast is at -1
>>> breakfast_foods[-1]
'Toast'
list中某一段的元素可以透過_切片表示法_（<list>[start:stop]）來存取。_切片_是指在位置index上、滿足start <= index < stop的一段元素序列。_切片_會回傳被「切出」項目的複本，不會修改原本的list。
也可以使用step參數[start:stop:step]來「跳過」或篩選list元素（例如step為 2 時，會選取範圍中每隔一個的元素）：
>>> colors = ["Red", "Purple", "Green", "Yellow", "Orange", "Pink", "Blue", "Grey"]
# If there is no step parameter, the step is assumed to be 1.
>>> middle_colors = colors[2:6]
>>> middle_colors
['Green', 'Yellow', 'Orange', 'Pink']
# If the start or stop parameters are omitted, the slice will
# start at index zero, and will stop at the end of the list.
>>> primary_colors = colors[::3]
>>> primary_colors
['Red', 'Yellow', 'Blue']
操作陣列
對陣列使用內建的sum()函式，會回傳陣列中所有數字的總和：
>>> number_list = [1, 2, 3, 4]
>>> sum(number_list)
10
你也可以用len()函式取得陣列的_長度_：
>>> long_list = ["A", "B", "C", "D", "E", "F", "G", "H", "I", "J"]
>>> len(long_list)
10
陣列也可以用各種方式合併：
# Using the plus + operator unpacks each list and creates a new list, but it is not efficient.
>>> new_via_concatenate = ["George", 5] + ["cat", "Tabby"]
>>> new_via_concatenate
['George', 5, 'cat', 'Tabby']
# Likewise, using the multiplication operator * is the equivalent of using + n times.
>>> first_group = ["cat", "dog", "elephant"]
>>> multiplied_group = first_group * 3
>>> multiplied_group
['cat', 'dog', 'elephant', 'cat', 'dog', 'elephant', 'cat', 'dog', 'elephant']
陣列提供_疊代器_，可以像其他_序列型別_一樣用迴圈走訪。
# Looping through the list and printing out each element.
>>> colors = ["Orange", "Green", "Grey", "Blue"]
>>> for item in colors:
... print(item)
...
Orange
Green
Grey
Blue
如果想更深入了解loops和iterators，就完成loops概念吧。
學習練習
