Python File Handling

• Python offers several functions for file manipulation: creating, reading, updating, and deleting.
• The open() function is key for file operations, requiring the filename and mode as parameters.

File Opening Modes

• "r" mode: Opens a file for reading, the default mode; an error occurs if the file does not exist.
• "a" mode: Opens a file for appending new content to the end without replacing existing content; creates the file if it does not exist.
• "w" mode: Opens a file for writing; creates the file if it does not exist.
• "x" mode: Creates a new file; using the open() method with "x" parameter, returns an error if the file already exists.

Default Values

• When opening a file for reading, it is enough to specify the name of the file.
• "r" for read and "t" for text are the default values, so they can be ommitted.
• Example:
  • f = open("demofile.txt") is enough for reading.
  • f = open("demofile.txt", 'rt') is identical.

Opening and Reading from a Server File

• Theopen() function returns a file object with a read() method to read the content, like this:

f = open("C:\\Users\bilal\demofile.txt", "r")
print(f.read())

• The read() method by default returns all text, but you can also specify the number of characters to return.
• f.read(5) returns the first 5 characters of the file.
• The readline() method reads a single line from the file.

Closing Files

• It is important to close files after use.
• Example use

f = open ("c:\\demofile.txt", "r")
print(f.readline())
f.close()

Iterating Over Lines

• Looping through a file line by line:

f = open ("c:\\demofile.txt", "r")
for x in f:
    print(x)
f.close()

Overwriting Content

• Writing to a file using "w" deletes all previous content.

Deleting Files

• To delete a file, the OS module must be imported, and the os.remove() function used.
  • Example:

import os
os.remove("demofile.txt")

Deleting Folders

• To delete an entire folder, use the os.rmdir() method.
  • Example:

import os
os.rmdir("myfolder") #Remove Directory entire folder

Renaming files

• The rename() method takes two arguments: the current filename and the new filename.

import os
os.rename('old_file.txt', 'new_file.txt')

Automatic Closing

• Python offers auto-closing of files via the with syntax which simplifies file handling.
• This allows you to open do operations and close, without a manual close.
• Example:

with open('my_path/my_file.txt', 'r') as file:
    file_data = file.read()

Using "With" to Write

with open("c:\\demofile.txt", "w") as file:
    file.write("Hello, this text is written using 'with' statement.\n")
    file.write("It handles file closing automatically!")

• Using "with" mode deletes content.