python-自定義異常

• 我們在編寫代碼時，可以自定義異常，這樣方便查錯

• 直接看例子就可以

  • 這個例子是寫一個函數來打印指定文件的第一行
  • 使用錯誤代碼和錯誤說明描述我們自己定義的異常

  # 測試準備
  dream:tmp dream$ cd /tmp/testForException/  # 測試的目錄
  dream:testForException dream$ touch file1.txt  # file1.txt爲空
  dream:testForException dream$ echo -e 'aaaa\nbbbb\ncc' > file2.txt  # file2.txt寫入信息
  dream:testForException dream$ ls
  file1.txt file2.txt
  dream:testForException dream$ cat file2.txt 
  aaaa
  bbbb
  cc
  
  
  # 測試代碼
  In [1]: import os
  
  In [3]: os.chdir('/tmp/testForException/')
  
  In [4]: os.getcwd()
  Out[4]: '/private/tmp/testForException'
  
  In [5]: os.system('ls')
  file1.txt file2.txt
  Out[5]: 0
  
  In [9]: class DirNotExist(Exception):  # 自定義的異常都是基礎Exception類的
     ...:     def __init__(self):
     ...:         self.code = 100
     ...:         self.description = '該文件所在目錄不存在'
     ...:         
  
  In [10]: class FileNotExist(Exception):
      ...:     def __init__(self):
      ...:         self.code = 101
      ...:         self.description = '該文件不存在'
      ...:          
  
  In [11]: class FileIsEmpty(Exception):
      ...:     def __init__(self):
      ...:         self.code = 101
      ...:         self.description = '該文件爲空'
      ...:          
  
  In [24]: def printOneLine(file_path): 
      ...:     '''                
      ...:     該函數作用爲打印指定文件的第一行，錯誤類型如下：
      ...:     code=100-->文件所在目錄不存在  
      ...:     code=101-->文件不存在
      ...:     code=102-->文件爲空
      ...:     '''
      ...:     try:
      ...:         if not os.path.exists(os.path.dirname(file_path)):
      ...:             raise DirNotExist()
      ...:         if not os.path.exists(os.path.basename(file_path)):
      ...:             raise FileNotExist()
      ...:         if os.path.getsize(file_path) == 0:
      ...:             raise FileIsEmpty()
      ...:         with open(file_path, mode='r', encoding='utf-8') as f:
      ...:             print(f.readline())
      ...:         
      ...:     except DirNotExist as e:
      ...:         print(e.code, ': ', e.description)
      ...:     except FileNotExist as e:
      ...:         print(e.code, ': ', e.description)
      ...:     except FileIsEmpty as e:
      ...:         print(e.code, ': ', e.description)
      ...:     except Exception as e:
      ...:         print(e)
      ...:      
        
  
  # 測試結果
  In [25]: printOneLine('/tmp/testForException/file1.txt')
  101 :  該文件爲空
  
  In [26]: printOneLine('/tmp/testForException/file2.txt')
  aaaa
  
  
  In [27]: printOneLine('/tmp/testForException/file3.txt')
  101 :  該文件不存在
  
  In [28]: printOneLine('/tmp/xxx/file3.txt')
  100 :  該文件所在目錄不存在
  

  • 當執行raise DirNotExist()時，先實例化該對象，然後再拋出異常對象
  • 被拋出的異常對象會被下面的except ·· as e按順序查看是否能捕獲