File Handling in Python

Why File Handling Matters

Real programs need to read from and write to files — logs, configuration, datasets, reports. Python makes this simple with the built-in open() function.

Opening a File

file = open("data.txt", "r")   # open in read mode
content = file.read()
file.close()                     # always close the file when done

File Modes

The with Statement (Recommended)

Using with automatically closes the file for you — even if an error occurs. This is the recommended way to handle files in Python:

with open("data.txt", "r") as file:
    content = file.read()
    print(content)
# file is automatically closed here

Reading a File

with open("data.txt", "r") as file:
    print(file.read())          # read entire file as one string

with open("data.txt", "r") as file:
    print(file.readline())      # read a single line

with open("data.txt", "r") as file:
    for line in file:            # loop through file line by line
        print(line.strip())

Writing to a File

with open("notes.txt", "w") as file:
    file.write("Learning Python at CodingNow\n")
    file.write("File handling is easy!\n")

Careful: mode "w" completely overwrites the existing file content. Use "a" if you want to add to it instead.

Appending to a File

with open("notes.txt", "a") as file:
    file.write("Adding one more line.\n")

Checking If a File Exists

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

Key Takeaways

• Always prefer with open(...) as file: — it closes the file automatically
• Mode "w" overwrites a file; mode "a" appends to it
• Loop through a file object directly to read it line by line efficiently