Python – File 物件 & Open 函式

測試環境為 CentOS 8 x86_64 (虛擬機)

參考文章 – https://medium.com/ccclub/ccclub-python-for-beginners-tutorial-bf0648108581

Python 提供 檔案物件 file object 來存取檔案.

開啟檔案 open()

open(file, mode='模式')

有以下模式

• r – Read 唯讀模式.
• w – Write 寫入模式,當檔案不存在時新增檔案,檔案存在時覆寫原檔案.
• x – open for exclusive creation, failing if the file already exists
• a – append 附加模式,新增內容到檔案的後面.
• b – binary mode
• t – text mode (default)
• + – open for updating (reading and writing)

檔案範本

[root@localhost ~]# cat PythonSample.txt 
Python number one
Taiwan number one

直接進入 Python command 模式,來試試不同讀取檔案的方式.

[root@localhost ~]# python3
Python 3.6.8 (default, Mar 25 2022, 11:15:52) 
[GCC 8.5.0 20210514 (Red Hat 8.5.0-10)] on linux
Type "help", "copyright", "credits" or "license" for more information.

• file.read()

  f1=open('PythonSample.txt','r')
  words = f1.read()
  type(words)
  f.close()
  

  執行結果

  >>> f1=open('PythonSample.txt','r')
  >>> words = f1.read()
  >>> print(words)
  Python number one
  Taiwan number one
  
  >>> type(words)
  <class 'str'>
  
  >>> f.close()
  

• file.readline()
  每次讀一行.

  f1=open('PythonSample.txt','r')
  words = f1.readline()
  print(words)
  type(words)
  f.close()
  

  執行結果

  >>> f1=open('PythonSample.txt','r')
  >>> words = f1.readline()
  >>> print(words)
  Python number one
  
  >>> type(words)
  <class 'str'>
  
  >>> f.close()
  

• file.readlines()
  讀取的資料存放成 list (串列).

  f1=open('PythonSample.txt','r')
  for lines in f1.readlines():
      print(lines)
  type(words)
  f.close()
  

  執行結果

  >>> f1=open('PythonSample.txt','r')
  >>> for lines in f1.readlines():
  ...     print(lines)
  ... 
  Python number one
  
  Taiwan number one
  
  >>> type(words)
  <class 'list'>
  >>> f.close()
  

• file.write()
  寫入檔案.

  f = open('PythoneWrite.txt', 'w')
  f.write("Write file")
  f.close()
  

  執行結果

  >>> f = open('PythoneWrite.txt', 'w')
  >>> f.write("Write file")
  10
  >>> f.close()
  >>> 
  [2]+  已停止               python3
  [root@localhost ~]# cat PythoneWrite.txt
  Write file
  

• file.writelines()
  寫入檔案.其資料格式須為 list (陣列).

  f = open('PythoneWrite.txt', 'w')
  data1 = ["Python write file\n","Sample here"]
  f.writelines(data1)
  f.close()
  

  執行結果

  >>> f = open('PythoneWrite.txt', 'w')
  >>> data1 = ["Python write file\n","Sample here"]
  >>> f.writelines(data1)
  >>> f.close()
  >>> 
  [3]+  已停止               python3
  [root@localhost ~]# cat PythoneWrite.txt
  Python write file
  Sample here
  

• file.seek()
  有個指標來標記檔案目前在哪一行,指標在讀取所有資料後就會指向在檔案最後,再次去讀取檔案就讀不到資料(因為指標已經在最後了),須透過 seek()重新指定檔案的指標 (0 表示為檔案最前面).

  f1=open('PythonSample.txt','r')
  words = f1.read()
  print(words);
  
  words = f1.read()
  print(words);
  
  f1.seek(0)
  words = f1.read()
  print(words);
  

  執行結果

  >>> f1=open('PythonSample.txt','r')
  >>> words = f1.read()
  >>> print(words);
  Python number one
  Taiwan number one
  
  >>> words = f1.read()
  >>> print(words);
  
  >>> f1.seek(0)
  0
  >>> words = f1.read()
  >>> print(words);
  Python number one
  Taiwan number one
  

• file.tell()
  指出目前檔案指標( 0 表示檔案的最前面)在哪裡.

  f1=open('PythonSample.txt','r')
  words = f1.readline(3)
  print(words);
  print(f1.tell());
  

  執行結果

  >>> f1=open('PythonSample.txt','r')
  >>> words = f1.readline(3)
  >>> print(words);
  Pyt
  >>> print(f1.tell());
  3