Python 的迴圈結構

基本迴圈結構：

• Python 基本迴圈 while 結構：

  while (判斷式):
      執行程式內容
         :
         :
  

• Python 基本迴圈 for 結構：

  for 變數名稱 in 有多個內容的變數:
      執行程式內容
         :
         :
  

• Python 迴圈常用的關鍵字：

  關鍵字名稱	說明
  break	中斷迴圈執行
  continue	跳過迴圈執行
  else	檢查迴圈運作

快速測試：

1. 使用互動式指令：

   #python3
   Python 3.4.3 (default, Jan 26 2016, 02:25:35)
   [GCC 4.8.5 20150623 (Red Hat 4.8.5-4)] on linux
   Type "help", "copyright", "credits" or "license" for more information.
   >>>
   

2. While 迴圈基本練習：

   >>> count = 1
   >>> while count <= 5:
   ...    print("Right")
   ...    count += 1
   ... else:
   ...    print("Left")
   ...
   (執行結果)
   Right
   Right
   Right
   Right
   Right
   Left
   
   

3. 離開互動式指令：

   >>> quit()
   

4. 編寫 python 程式檔案(while 迴圈)：

   $ vim while1.py
   count = 1
   while count <= 5:
     print(count,"\t","Right")
     if (count == 3):
       print("break")
       break
     count += 1
   else:
     print("Left")
   

5. 執行 python 程式檔案：

   $ python3 while1.py
   1        Right
   2        Right
   3        Right
   break
   
   

6. 編寫 python 程式檔案(For 迴圈)：

   $ vim for1.py
   cats = ["Peter","John","Tom","Judy"]
   for cat in cats:
     if cat == "Tom":
       print(cat,"\t","is Running Away ...")
       continue
     print (cat, "\t","is sitting here..")
   else:
     print ("Cats are All")
   
   

7. 執行 python 程式檔案：

   $ python3 for1.py
   Peter    is sitting here..
   John     is sitting here..
   Tom      is Running Away ...
   Judy     is sitting here..
   Cats are All
   
   

8. 編寫更複雜的 For 迴圈程式：

   $ vim for2.py
   cats = {'Persian':'Peter',
           'Aegean':'Judy'}
   for cat in cats.values():
     print ("Cats are :", cat)
   
   for kinds in cats.keys():
     print ("Cats' catogary has:", kinds)
   
   for catogary, cat in cats.items():
     print (catogary," has the cats:",cat)
   
   

9. 執行 python 程式檔案：

   $ python3 for2.py
   Cats are : Judy
   Cats are : Peter
   Cats' catogary has: Aegean
   Cats' catogary has: Persian
   Aegean  has the cats: Judy
   Persian  has the cats: Peter