Python File Handling

Python File Handling Part 1

File handling is one of the important feature in programming languages. Python provides a way to handle(read, write & modify) both text files as well as binary files. This tutorial will cover open() function in detail.

➠ There are various functions available in Python for File handling. Click the function to get more detail about that function.

• Open
• Read
• ReadLine
• ReadLines
• Seek
• Tell
• Peek
• Write
• WriteLines
• Flush
• Close

➠ Open: The open() function takes two parameters i.e. filename and mode. Out of the 2 parameters, filename is mandatory parameter and mode is optional parameter. There are 2 variations of open() function and their syntax are

• • Syntax 1: Directly assigning file pointer to a variable using open() function. And file is opened in this way then file is required to be closed using close() function once required operations are done.

    fileVariableName = open( filename_with_full_path, open_mode)
    .
    .
    fileVariableName.close()
    

    
    
  • Syntax 2: 'with open()' function can be used when file operations need to be done within open file block. And file will be closed automatically once the block execution is over.

    with open(filename_with_full_path, open_mode) as fileVariableName:
        .
        .
    

  
  ⇰ There are four different modes to open a file and those are listed below

  • Mode	Description / Functionality
    r	This is default and opens a file in reading mode. It will result in error if the file does not exist.
    a	Opens a file in append mode. It will create file if the file does not exist.
    w	Opens a file in writing mode. It will create file if the file does not exist.
    x	Opens a file in writing mode(same as 'w'). It will result in error if the file exists.
    +	Opens a file in read/write or write/read or append/read mode depending on the other mode specified. This must be used along with append(a), read(r) or write(w) mode.

  
  ⇰ In addition to read & write mode, users can also specify if the file should be handled as binary or text mode.

  • Mode	Description / Functionality
    t	This is default and it is meant to open a file in text mode for text related operations.
    b	It meant to open a file in binary mode for binary related operations(e.g. working with images).

  
  
  ⇰ Some of the examples for the open() function and its mode. Click here to download test file used in the examples.
  • Read Mode Example 1:

    
    fileVar = open("/complete_path_to_file/pythonTest.txt", "r")
    print(fileVar.read())
    fileVar.close()
    
    Output: 
    Line 1: This is Python File Handling
    Line 2: This is Python File Handling Testing File
    

  • Read Mode Example 2:

    
    with open("/complete_path_to_file/pythonTest.txt", "r") as fileVar:
        print(fileVar.read())
    
    
    Output: 
    Line 1: This is Python File Handling
    Line 2: This is Python File Handling Testing File
    

  • Write Mode Example 3: Write mode will create 'pythonTestWrite.txt' file and overwrite file if already exists.

    
    fileVar = open("/complete_path_to_file/pythonTestWrite.txt", "w")
    fileVar.write('This is Python File Writing\n')
    fileVar.close()
    
    
    Output: 
    *******pythonTestWrite.txt content********
    This is Python File Writing <newline Character>
    ******************************************
    

  • X(create) Mode Example 4: X mode will result in error as file 'pythonTest.txt' already exists.

    
    fileVar = open("/complete_path_to_file/pythonTest.txt", "x")
    
    
    Output: 
    FileExistsError: [Errno 17] File exists: '/complete_path_to_file/pythonTest.txt'
    

  • Append Mode Example 5: Append mode will always append data at the end the file (in this case 'pythonTestWrite.txt').

    
    fileVar = open("/complete_path_to_file/pythonTestWrite.txt", "a")
    fileVar.write('\nThis is another line')
    fileVar.close()
    
    
    Output: 
    *******pythonTestWrite.txt content********
    This is Python File Writing
    This is another line
    ******************************************
    

  • Read/Text Mode Example 6: Example showing file opened in read & text mode specifically.

    
    fileVar = open("/complete_path_to_file/pythonTestWrite.txt", "rt")
    print(fileVar.readline())
    fileVar.close()
    
    
    Output: 
    This is Python File Writing <newline Character>
    

  • Read/Binary Mode Example 7: Example showing image file opened in read & binary mode.

    
    fileVar = open("/Users/Pradeep/Desktop/websites/dbmstutorials/favicon.ico", "rb")
    print(fileVar.read(10))
    fileVar.close()
    
    
    Output: 
    b'\x00\x00\x01\x00\x01\x00  \x00\x00'
    
    
    
    ==> If users will try to read binary file in text format then Python will throw below error.
    
    Traceback (most recent call last):
      File "", line 1, in 
      File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/codecs.py", line 322, in decode
        (result, consumed) = self._buffer_decode(data, self.errors, final)
    UnicodeDecodeError: 'utf-8' codec can't decode byte 0xa8 in position 14: invalid start byte
    
    

  • Example 8 : Openning text file in binary read mode.
    • Example 8.1: If text file is opened in binary mode then users will notice b' string around the output. Therefore be careful while opening text file in binary mode.

      
      fileVar = open("/complete_path_to_file/pythonTest.txt", "rb")
      print(fileVar.readline())
      fileVar.close()
      
      Output: 
      b'Line 1: This is Python File Handling\n'
      

    • Example 8.2: User can use decode() function to convert binary quote into normal text.

      
      fileVar = open("/complete_path_to_file/pythonTest.txt", "rb")
      print(fileVar.readline().decode('utf-8'))
      
      Output: 
      Line 1: This is Python File Handling <newline Character>
      
      

  • Read/Write Mode Example 9: Example showing file opened in read/write mode. By default if user writes data to the file in this mode then it will start writing from beginning and overwrite existing characters. This can be resolved by moving cursor to the end of file.

    
    fileVar = open("/complete_path_to_file/pythonTestWrite.txt", "r+")
    fileVar.write('This will overwrite characters')
    print(fileVar.read(15))
    fileVar.close()
    
    
    *****pythonTestWrite.txt content Before********
    This is Python File Writing
    This is another line
    ***********************************************
    
    Output: 
    This will overw
    
    *******pythonTestWrite.txt content After********
    This will overwrite characters
    s is another line
    ************************************************
    

  • Write/Read Mode Example 10: Example showing file opened in write/read mode. This will overwrite all the content of file but newly written data can be read by moving cursor back to required position using seek() function.

    
    fileVar = open("/complete_path_to_file/pythonTestWrite.txt", "w+")
    fileVar.write('This will overwrite characters')
    fileVar.close()
    
    
    *****pythonTestWrite.txt content Before********
    This is Python File Writing
    This is another line
    ***********************************************
    
    Output: 
    *******pythonTestWrite.txt content After********
    This will overwrite characters
    ************************************************
    

  • Append/Read ModeExample 11: Example showing file opened in append/read mode. This mode will always append data at the end of file and does not overwrite the existing data. Data can be read by moving cursor back to required position using seek() function.

    
    fileVar = open("/complete_path_to_file/pythonTestWrite.txt", "a+")
    fileVar.write('\nThis will append at the end of file')
    fileVar.close()
    
    
    *****pythonTestWrite.txt content Before********
    This is Python File Writing
    This is another line
    ***********************************************
    
    Output: 
    *******pythonTestWrite.txt content After********
    This is Python File Writing
    This is another line
    This will append at the end of file
    ************************************************
    

****Visit File Handling part 2 for more functions