Python File Handling

Python File Handling Part 2

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 read(), readlines(), seek() and tell() functions 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

➠ Read: The read() function can be used to read the content of file. The read() function can takes one optional parameter i.e Integer parameter which will return 'n' characters from the postion of cursor. By default, content of open file can be read only once as read() function will leave the cursor at the end of the file.

• Example 1: Even mode 'r' is not specified, it will open file in read mode as it is default mode.

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

• Example 2: This will read only upto 22 characters from beginning of cursor.

  
  fileVar = open("/complete_path_to_file/pythonTest.txt", "r")
  print(fileVar.read(22))
  fileVar.close()
  
  
  Output: 
  Line 1: This is Python
  

➠ ReadLine: The readline() function can be used to read one line at a time from the file, starting from the beginning of cursor till the end of the line. Output of the readline() function also includes the newline character if present as line separator.

• Example 1:

  
  fileVar = open("/complete_path_to_file/pythonTest.txt", "r")
  print(fileVar.readline())
  fileVar.close()
  
  Output: 
  Line 1: This is Python File Handling <newline Character>
  
  

• Example 2: This will read from 16th character till the end of line.

  
  fileVar = open("/complete_path_to_file/pythonTest.txt", "r")
  fileVar.seek(16)   #moving the cursor to 16th character
  print(fileVar.readline())
  fileVar.close()
  
  
  Output: 
  Python File Handling <newline Character>
  
  

➠ ReadLines: The readlines() function returns each line (beginning from the start of cursor till end of file) as items in the list. Output of the readlines() function also includes the newline character if present as line separator.

• Example 1:

  
  fileVar = open("/complete_path_to_file/pythonTest.txt", "r")
  print(fileVar.readlines())
  fileVar.close()
  
  Output: 
  ['Line 1: This is Python File Handling\n', 'Line 2: This is Python File Handling Testing File']
  

• Example 2: This will read from 16th character till the end of file.

  
  fileVar = open("/complete_path_to_file/pythonTest.txt", "r")
  fileVar.seek(16)   #moving the cursor to 16th character
  print(fileVar.readlines())
  fileVar.close()
  
  
  Output: 
  ['Python File Handling\n', 'Line 2: This is Python File Handling Testing File']
  

• Example 3: Storing the lines of files into a list variable and reading 2 line.

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

• Example 4: Reading file lines using for loop until end of the file.

  
  fileVar = open("/complete_path_to_file/pythonTestWrite.txt", "r")
  for x in fileVar:
      print(x)
  
  
  Output: 
  This is Python File Writing
  
  This is Python's second File Writing line
  

➠ Seek: The seek() function can be used to move cursor at the required position.

• The seek() function takes one integer parameter(position parameter) to move cursor at the required position and second one 'whence' is optional parameter which is applicable only for binary mode reading.
• Whence parameter can have 3 possible values(0, 1, 2)
  • 0 == This is default and moves cursor as per the position from start of file. Position parameter value must be zero or positive if whence 0 is specified.
  • 1 == Moves the cursor as per the position from current postion of cursor. Position parameter value may be negative if whence 1 is specified.
  • 2 == Moves the cursor as per the position from end of file. Position parameter value is generally negative if whence 2 is specified.
• The position parameter is interpreted relative to the position indicated by whence.
• The seek() function returns the absolute position(as integer) of cursor where it was moved.
• File content can be read again by moving(from end of file) the cursor to the beginning of the file.
  • Example 1: Reading the file again after setting the cursor to the beginning of the file.

    
    fileVar = open("/complete_path_to_file/pythonTest.txt", "r")
    print(fileVar.read())
    fileVar.seek(0)   #moving the cursor to beginning of file
    print(fileVar.read())   #Reading the file again
    fileVar.close()
    
    Output: 
    Line 1: This is Python File Handling
    Line 2: This is Python File Handling Testing File
    0
    Line 1: This is Python File Handling
    Line 2: This is Python File Handling Testing File
    

  • Example 2: This will move cursor to 16th character and read will read from 16th character till the end of file.

    
    fileVar = open("/complete_path_to_file/pythonTest.txt", "r")
    fileVar.seek(16)   #moving the cursor to 16th character
    print(fileVar.readline())
    fileVar.close()
    
    Output: 
    Python File Handling <newline Character>
    
    

  • Examples with Whence : Openning text file in binary read mode to demonstrate usage of whence.
    • Example 3.1: Going back 11 characters from the current cursor position. Decode is used to convert binary data to text & reading first 27 characters

      
      fileVar = open("/complete_path_to_file/pythonTest.txt", "rb")
      print(fileVar.read(27).decode('utf-8'))
      fileVar.seek(-11,1)  
      print(fileVar.read(20).decode('utf-8'))
      fileVar.close()
      
      Output: 
      Line 1: This is Python File
      16
      Python File Handling
      

    • Example 3.2: Going back 12 characters from the end of the file position.

      
      fileVar = open("/complete_path_to_file/pythonTest.txt", "rb")
      print(fileVar.read(27).decode('utf-8'))
      fileVar.seek(-12,2)  
      print(fileVar.read(20).decode('utf-8'))
      fileVar.close()
      
      Output: 
      Line 1: This is Python File Handling <newline Character>
      
      

➠ Tell: The tell() function can be used to get the current position of the cursor in the file.

• Example 1:

  
  fileVar = open("/complete_path_to_file/pythonTest.txt", "r")
  str_line1 = fileVar.readline()
  print(fileVar.tell())
  
  Output:  37
  



****Visit File Handling part 3 for more functions