What is File Handling in Python?

File handling allows you to create, read, write, append, and delete files (text or binary) using Python’s built-in functions. It's essential for tasks like reading logs, saving data, or processing files.

1. Opening a File with open()

file = open("example.txt", "r")  # "r" means read mode
print(file.read())
file.close()

Modes:

2. Reading a File

Read Entire File

with open("example.txt", "r") as f:
   content = f.read()
   print(content)

Read Line by Line

with open("example.txt", "r") as f:
   for line in f:
       print(line.strip())

Read First N Characters

with open("example.txt", "r") as f:
   print(f.read(10))  # Read first 10 chars

3. Writing to a File (w)

with open("output.txt", "w") as f:
   f.write("Hello World\n")
   f.write("Welcome to Python!")

Note: This will overwrite the file if it exists.

4. Appending to a File (a)

with open("output.txt", "a") as f:
   f.write("\nThis is an additional line.")

5. Writing a List to a File

lines = ["Line 1\n", "Line 2\n", "Line 3\n"]
with open("list.txt", "w") as f:
   f.writelines(lines)

6. Reading as a List of Lines

with open("list.txt", "r") as f:
   lines = f.readlines()
   print(lines)

Output:

['Line 1\n', 'Line 2\n', 'Line 3\n']

7. Checking If File Exists

import os
if os.path.exists("list.txt"):
   print("File found!")
else:
   print("File not found.")

8. Deleting a File

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

Note: Always check existence before deleting!

9. Create a File If Not Exists (x)

with open("newfile.txt", "x") as f:
   f.write("New file created.")

10. File Modes Summary Table

Example: Copy Content from One File to Another

with open("source.txt", "r") as src, open("dest.txt", "w") as dest:
   for line in src:
       dest.write(line)