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DAY 11
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Python 學習筆記系列 第 11

Day11 Python 基礎 - 列表的使用

如果想要存所有 Marvel's The Avengers 角色的人名,該如何存呢?請用目前已學到的知識來實做…

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

names = "Rogers Stark Thor Loki Natasha"

目前已存了五個人,透過空白來區分(也可以用逗號),但該如何去取某一個人的值!?因為咱們已經把這五個人的人名存在一個變量裡了,所以沒辦法取,除非…可以像 Shell Script 透過 sed or awk 去做區分(喂~不能這樣做),想改也沒辦法改,實務上,我們想存很多的訊息,並且透過字符串來存,就面臨了二個問題,一是不好存,二是不好改,所以後來發展出了新的數據類型,就叫 列表,在 Python 裡,使用列表時,就請用 [](中括號)

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

names = "Rogers Stark Thor Loki Natasha"
names = []

print(names)

---------------執行結果---------------
[]

Process finished with exit code 0

這樣就打印出來一個空的列表,接下來把剛剛的人名給存在這列表裡吧…

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

names = "Rogers Stark Thor Loki Natasha"
names = ["Rogers", "Stark", "Thor", "Loki", "Natasha"]

print(names)

---------------執行結果---------------

['Rogers', 'Stark', 'Thor', 'Loki', 'Natasha']

Process finished with exit code 0

這樣就把人名存進去了,接下來我們來取其中一個人名好了,抓 Rogers好了,該怎麼取呢?

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

names = "Rogers Stark Thor Loki Natasha"
names = ["Rogers", "Stark", "Thor", "Loki", "Natasha"]

print(names["Rogers"])

---------------執行結果---------------

Traceback (most recent call last):
  File "/Users/ironman/python/names.py", line 7, in <module>
    print(names["Rogers"])
TypeError: list indices must be integers or slices, not str

Process finished with exit code 1

結果發現報錯 TypeError: list indices must be integers or slices, not str,是因為不能這樣取值的,正確取值應該是…

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

names = "Rogers Stark Thor Loki Natasha"
names = ["Rogers", "Stark", "Thor", "Loki", "Natasha"]

print(names[0])

---------------執行結果---------------

Rogers

Process finished with exit code 0

這樣就取出來了,但為什麼會是0呢? 0就代表 Rogers在這個列表中,從左到右開始的第一個位置,但在電腦存數據時,不是從1開始算的,是從0開始算起的,因為二進制使用的第一個狀態就是0,所以從0開始算的,因此,我們可以透過位置來取得相對應的值。

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

names = "Rogers Stark Thor Loki Natasha"
names = ["Rogers", "Stark", "Thor", "Loki", "Natasha"]

print(names[0], names[1])

---------------執行結果---------------

Rogers Stark

Process finished with exit code 0

接下來有沒有辦法一次就把 StarkThor 給取出來?

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

names = "Rogers Stark Thor Loki Natasha"
names = ["Rogers", "Stark", "Thor", "Loki", "Natasha"]

print(names[0], names[1])
print(names[1:2])

---------------執行結果---------------

Rogers Stark
['Stark']

Process finished with exit code 0

咦~怎麼只出現 Stark ?那在往後取一位試試…

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

names = "Rogers Stark Thor Loki Natasha"
names = ["Rogers", "Stark", "Thor", "Loki", "Natasha"]

print(names[0], names[1])
print(names[1:2])

---------------執行結果---------------

Rogers Stark
['Stark', 'Thor']

Process finished with exit code 0

哦…這樣就取出來正確的了,那有沒有發現一個問題,就是只有顧到(包括) 起始位置,而沒有顧到(不包括) 結束位置 ,所以我們叫這個是 顧頭不顧尾 ,如果你要取的位置是連續的就可以用這個方式,而這個方式就叫做 slices(切片)

假設今天我有一個很長的列表,不知道有幾個,但想取最後一個,該怎麼取呢?我們依上面的代碼,先取出最後一個值

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

names = "Rogers Stark Thor Loki Natasha"
names = ["Rogers", "Stark", "Thor", "Loki", "Natasha"]

print(names[0], names[1])
print(names[1:3])
print(names[4])        # 在已知可數的情況下,就是我們一般取最後一個值的用法

---------------執行結果---------------

Rogers Stark
['Stark', 'Thor']
Natasha

Process finished with exit code 0

在不可數的情況下,也是一般較常用的寫法是

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

names = "Rogers Stark Thor Loki Natasha"
names = ["Rogers", "Stark", "Thor", "Loki", "Natasha"]

print(names[0], names[1])
print(names[1:3])
print(names[4])
print(names[-1])

---------------執行結果---------------

Rogers Stark
['Stark', 'Thor']
Natasha
Natasha

Process finished with exit code 0

正的就是從左到右取值,負的就是從右到左取值,那如果接下想要取一次取最後二個值,該怎麼取呢?

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

names = "Rogers Stark Thor Loki Natasha"
names = ["Rogers", "Stark", "Thor", "Loki", "Natasha"]

print(names)
print(names[-1:-3])

---------------執行結果---------------

['Rogers', 'Stark', 'Thor', 'Loki', 'Natasha']
[]

Process finished with exit code 0

為什麼取出空列表哩,主要是因為 切片還是一樣是 從左往右數來取得數值的,所以我們應該要寫成-3開始取值

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

names = "Rogers Stark Thor Loki Natasha"
names = ["Rogers", "Stark", "Thor", "Loki", "Natasha"]

print(names)
print(names[-3:-1])

---------------執行結果---------------

['Rogers', 'Stark', 'Thor', 'Loki', 'Natasha']
['Thor', 'Loki']

Process finished with exit code 0

又不對了,別忘記了,切片取值是顧頭不顧尾, 所以才會取出 ThorLoki,那在修改一下,參考下圖說明

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

names = "Rogers Stark Thor Loki Natasha"
names = ["Rogers", "Stark", "Thor", "Loki", "Natasha"]

print(names)
print(names[-2:-1])

---------------執行結果---------------

['Rogers', 'Stark', 'Thor', 'Loki', 'Natasha']
['Loki']

Process finished with exit code 0

又不對了,因為 切片是顧頭不顧尾,但又想取最後一個值,又該怎麼辦?

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

names = "Rogers Stark Thor Loki Natasha"
names = ["Rogers", "Stark", "Thor", "Loki", "Natasha"]

print(names)
print(names[-2:])

---------------執行結果---------------

['Rogers', 'Stark', 'Thor', 'Loki', 'Natasha']
['Loki', 'Natasha']

Process finished with exit code 0

這樣就取到,有發現嗎?如果要取最後一個數值,其實 省略不打就可以取到了,那如果要正取0到3,同樣的也是可以省略0,代碼寫法如下

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

names = "Rogers Stark Thor Loki Natasha"
names = ["Rogers", "Stark", "Thor", "Loki", "Natasha"]

print(names)
print(names[:3])

---------------執行結果---------------

['Rogers', 'Stark', 'Thor', 'Loki', 'Natasha']
['Rogers', 'Stark', 'Thor']

Process finished with exit code 0

接下來那我們又想要多加入一個人,該怎麼寫呢?

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

names = "Rogers Stark Thor Loki Natasha"
names = ["Rogers", "Stark", "Thor", "Loki", "Natasha"]
names.append("Barton")

print(names)

---------------執行結果---------------

['Rogers', 'Stark', 'Thor', 'Loki', 'Natasha', 'Barton']

Process finished with exit code 0

append() 意思就是附加,而且是加在最後面的,那如果想要隨意放在列表的任一位置呢?

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

names = "Rogers Stark Thor Loki Natasha"
names = ["Rogers", "Stark", "Thor", "Loki", "Natasha"]
names.append("Barton")
names.insert(1, "Coulson")

print(names)

---------------執行結果---------------

['Rogers', 'Coulson', 'Stark', 'Thor', 'Loki', 'Natasha', 'Barton']

Process finished with exit code 0

insert() 就是插入任意你想要插入的位置,依上例代碼來說,就是要把 Coulson 插入到 Stark 前面,因此,填入的數字就 1,這樣就會插入在 Stark 前了,那如果要在新增一個人,到 Stark後面,又要怎麼寫呢?

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

names = "Rogers Stark Thor Loki Natasha"
names = ["Rogers", "Stark", "Thor", "Loki", "Natasha"]
names.append("Barton")
names.insert(1, "Coulson")
names.insert(3, "Fury")

print(names)

---------------執行結果---------------

['Rogers', 'Coulson', 'Stark', 'Fury', 'Thor', 'Loki', 'Natasha', 'Barton']

Process finished with exit code 0

那要怎麼列表中的人名做取代的呢?

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

names = "Rogers Stark Thor Loki Natasha"
names = ["Rogers", "Stark", "Thor", "Loki", "Natasha"]
names.append("Barton")
names.insert(1, "Coulson")
names.insert(3, "Fury")
names[2] = "Bruce"

print(names)

---------------執行結果---------------

['Rogers', 'Coulson', 'Bruce', 'Fury', 'Thor', 'Loki', 'Natasha', 'Barton']

Process finished with exit code 0

有發現了嘛, Stark 被取代成 Bruce了,這就是取代,那再來要怎麼刪除人名嗎?總共三種方法,這次刪除都以位置為 1Coulson 做示範

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

names = "Rogers Stark Thor Loki Natasha"
names = ["Rogers", "Stark", "Thor", "Loki", "Natasha"]
names.append("Barton")
names.insert(1, "Coulson")
names.insert(3, "Fury")
names[2] = "Bruce"

print(names)

# delete methods

# 1. names.remove("Coulson")

# 2. del names[1] = names.pop(1)

# 3. names.pop(1)

names.pop(1)

print(names)

---------------執行結果---------------

['Rogers', 'Coulson', 'Bruce', 'Fury', 'Thor', 'Loki', 'Natasha', 'Barton']
['Rogers', 'Bruce', 'Fury', 'Thor', 'Loki', 'Natasha', 'Barton']

Process finished with exit code 0

這三個方法都可以用來刪除,其中要特別說明的就是 pop() 這個刪除是最後一個,請看下圖跟代碼

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

names = "Rogers Stark Thor Loki Natasha"
names = ["Rogers", "Stark", "Thor", "Loki", "Natasha"]
names.append("Barton")
names.insert(1, "Coulson")
names.insert(3, "Fury")
names[2] = "Bruce"

print(names)

names.pop()

print(names)

---------------執行結果---------------

['Rogers', 'Coulson', 'Bruce', 'Fury', 'Thor', 'Loki', 'Natasha', 'Barton']
['Rogers', 'Coulson', 'Bruce', 'Fury', 'Thor', 'Loki', 'Natasha']

Process finished with exit code 0

那如果要在列表中,尋找特定的一個人名是在哪一個位置,那該怎麼找呢?這次我們來找 Loki 好了

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

names = "Rogers Stark Thor Loki Natasha"
names = ["Rogers", "Stark", "Thor", "Loki", "Natasha"]
names.append("Barton")
names.insert(1, "Coulson")
names.insert(3, "Fury")
names[2] = "Bruce"

print(names)
print(names.index("Loki"))

---------------執行結果---------------

['Rogers', 'Coulson', 'Bruce', 'Fury', 'Thor', 'Loki', 'Natasha', 'Barton']
5

Process finished with exit code 0

嗯,找到了,但如果我想找出位置後,並打印出相對應的值,該怎麼寫?

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

names = "Rogers Stark Thor Loki Natasha"
names = ["Rogers", "Stark", "Thor", "Loki", "Natasha"]
names.append("Barton")
names.insert(1, "Coulson")
names.insert(3, "Fury")
names[2] = "Bruce"

print(names)
print(names.index("Loki"))
print( names[names.index("Loki")] )

---------------執行結果---------------

['Rogers', 'Coulson', 'Bruce', 'Fury', 'Thor', 'Loki', 'Natasha', 'Barton']
5
Loki

Process finished with exit code 0

那如何在列表中,查詢有相同人名的有幾個?

#!/usr/bin/env python3
# -*- coding:utf-8 -*-

names = "Rogers Stark Thor Loki Natasha"
names = ["Rogers", "Stark", "Thor", "Loki", "Natasha", "Coulson"]
names.append("Barton")
names.insert(1, "Coulson")
names.insert(3, "Fury")
names[2] = "Bruce"

print(names)
print(names.count("Coulson"))

---------------執行結果---------------

['Rogers', 'Coulson', 'Bruce', 'Fury', 'Thor', 'Loki', 'Natasha', 'Coulson', 'Barton']
2

Process finished with exit code 0

呼,今天好想發懶哦…冏,一個很適合睡覺的天氣


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Day10 Python 基礎 - bytes數據類型
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Day12 Python 基礎 - 列表的使用_v2
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