String - HackMD

# String 字串 --- ## 其實你看過囉 - print("Helloworld") - "Helloworld" ---- ## What's string? - " " 跟 ' ' 包起來的東西 - e.g. "123", 'hi' ---- ## 隨堂練習-1 以下何者是string呢? - "123" - \"123 " " - "123'123"' - '213213'"' ---- ## Solution - "123" 正解 - "123"" - 最後一個"沒有對到 - "123'123"' - 最後一個'沒有對到 - '213213'"' - "跟'都沒對到 ---- ## 日常生活中的string - 密碼學(凱薩加密) - Tqspvut -> Sprouts - 資料格式轉換 - "10 : 10 : 10" -> "10h 10m 10s" --- ## String vs list ---- ## 共通點-1 - len - len("123") => 3 - len([1,2,3]) => 3 - index - "123"[1] => "2" - [1,2,3][1] => 2 - in - "123" in "123456" => True - 123 in [123,234,345] => True ---- ## 共通點-2 : Traverse ```python= for i in "123": print(i) for i in [1,2,3]: print(i) ``` ---- ## 非共通點 : Immutable 試試看以下的Code ```python= a = [1,2,3] a[2] = 1 b = "123" b[2] = "1" ``` ---- ## TypeError - 'str' object does not support item assignment - string裡的元件不能被更換 ![](https://i.imgur.com/7DwdSrp.png) --- ## 字串-四天王 - replace - split - find - join ---- ## [字串變數].replace() - string.replace(str1,str2) - 將string裡的str1都換成str2 ---- # 牛刀小試 ``` "112312312323".replace("123","") ``` 1. "123" 2. "" ---- ## Example ```python= a = "rilakeeeeeeee" print(a.replace("e","")) # rilak ``` ---- ## [字串變數].split() - string.split(str,n) - 從string裡所有str的地方斷開，最多斷n個，也可以不要寫n ---- ## Example ```python= a = "rilak,achin,pie,arbuz" a.split(",") # ["rilak","achin","pie","arbuz"] a.split(",",2) # ["rilak","achin","pie,arbuz"] ``` ---- ## [字串變數].find() - string.find(str,start) - 從第start個字開始找str，回傳其index，start可不填 ---- ## Example ```python= a = "rilak achine pie arbuz" a.find("e ") # 11 a.find("e ",12) #故意跳過第一個 # 15 ``` ---- ## 練習 - 3042 : 傳奇野豬騎士陳刀III - 3045 : 野豬騎士史記 I ---- ## [字串變數].join() - string.join(list) - 以string為連接字串，將list裡的東西串在一起 - Warning : list裡都要是字串 ---- ## Example ```python= a = ["hortune","rilak","sky","buzz"] ", ".join(a) # 'hortune, rilak, sky, buzz' ``` --- # Slice ---- ## 字元的list string其實某種意義上是字元的list，所以list的slicing操作都可以使用 ---- ### "字串變數"[start : end : change] - start : index 初始值 - end : index 終止值 - 開區間 - change : index 變化量 ---- ## Example ```python= a = "Hello world" a[:a.find(" ")] # "Hello" a[a.find(" ")+1:] # "world" a[::-1] # 翻轉 # "dlrow olleH" ``` --- ## String的雜function - upper - lower - isalpha ---- ## Example ```python= "hello".upper() # HELLO "HELLO".lower() # hello "123".isalpha() # False "abc".isalpha() # True ``` --- ## String 四則運算 - 加法 - 乘法 - 相等 - 不相等 ---- ## 加法 (concat) ```python= a = "Hi " b = "Sprouts" a + b # 'Hi Sprouts' ``` ---- ## 乘法 (duplicate) ```python= "MuQ" * 10 # "MuQMuQMuQMuQMuQMuQMuQMuQMuQMuQ" ``` ---- ## 相等 (equal) ```python= "123" == "321" # False "1" == "1" # True ``` ---- ## 不相等 ```python= "123" != "321" # True "1" != "1" # False ``` ---- ## 大於小於?? ```python= 10123123 > 11 # True "10123123" > "11" # False ``` ---- ## 字典序 - python的字串比較是一個字一個字依照ascii下去比，"1"跟"1"一樣大，於是比下一個字，"0"小於"1"，所以"11"比較大。 - 詳細可以去看Ascii跟ord和chr兩個function ---- ## 隨堂練習-2 - 3046 : 西瓜的名字 --- # Bonus!!! ---- ## Format String ---- ## 情境 - 資料格式轉換 - "10 : 10 : 10" -> "10h 10m 10s" ---- ## You write? ```python= string = "10 : 10 : 10" numbers = string.split(" : ") print(numbers[0]+"h ",numbers[1]+"m",numbers[2]+"s") ``` ---- ## Cons - 醜 - 麻煩 ---- ## Elegant Way ```python= string = "10 : 10 : 10" "{}h {}m {}s".format(*string.split(" : ")) ``` ---- # WTF ---- ## 關鍵字-1 format ---- ## 關鍵字-2 `{}` ---- ## 奇怪點 - *string.split(":") - 先不管他 ---- # 進入正題 ---- ## Example 把後面塞進去 ```python= "{}".format(1) # 1 "{} {}".format(1,2) # 1 2 ``` ---- ## 回到剛剛 ```python= string = "10 : 10 : 10" "{}h {}m {}s".format(*string.split(" : ")) ``` ### 想成 ```python= string = "10 : 10 : 10" "{}h {}m {}s".format(10,10,10) ``` ---- ## 小知識 : * - \* list可以用來展開list，然後當成function的input。 ---- ## Advance ```python "{} {}".format(1,2) # 1 2 "{0} {1}".format(1,2) # 1 2 "{1} {0}".format(1,2) # 2 1 ``` ---- ## More [pyformat](https://pyformat.info/) --- ## Things Not Mentioned - Ascii - 跳脫字元 ---- ## Homework - [通靈之塔-靈的力量](https://neoj.sprout.tw/problem/3056/)