Python Learning Series · @onlysamarrr · Day 26 / 30

Day 26: File Handling

Day 26 teaches file handling. open() opens a file: 'w' writes and erases old content, 'a' appends, 'r' reads. The with statement closes the file automatically, so you never forget close().

Phase: Intermediate · Reels: 126/450 – 130/450

Quick Answer

Day 26 teaches file handling. open() opens a file: 'w' writes and erases old content, 'a' appends, 'r' reads. The with statement closes the file automatically, so you never forget close().

What You Will Learn

open(..., "w") creates a new file or erases an existing file's content before writing.
open(..., "a") appends: old content stays, new content is added at the end.
encoding="utf-8" keeps Hindi and emoji text safe.
with closes the file automatically when its block ends, so close() cannot be forgotten.
readlines() returns all lines as a list; in the example there are 3 lines.

Code

with open("notes_demo.txt", "w", encoding="utf-8") as f:
    f.write("Line 1\nLine 2\n")
with open("notes_demo.txt", "a", encoding="utf-8") as f:
    f.write("Line 3\n")
with open("notes_demo.txt", encoding="utf-8") as f:
    lines = f.readlines()
print(len(lines))
print(lines)

Output

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

Code Explained, Line by Line

open(..., "w") creates a new file or erases an existing file's content before writing.
open(..., "a") appends: old content stays, new content is added at the end.
encoding="utf-8" keeps Hindi and emoji text safe.
with closes the file automatically when its block ends, so close() cannot be forgotten.
readlines() returns all lines as a list; in the example there are 3 lines.

Common Mistake: Mode 'w' deletes the file's old content immediately. To add without deleting, use 'a', or your data is gone.

Real-Life Use

Logs, notes apps and saved settings all write to files.

Practice Task: Build a notes app: save lines to a file, then count how many lines it has.

Test Yourself — MCQs

Select (tick) an option, then tap Check answer to see instantly whether your answer is right or wrong, with an explanation. You can change your answer and check again.

Q1. What does open("f.txt", "w") do to existing content?

A. Keeps it B. Appends to it C. Erases it D. Nothing

Q2. Which mode appends without erasing?

A. "w" B. "r" C. "a" D. "x"

Q3. Why use with when opening a file?

A. It is faster B. It closes the file automatically C. It encrypts the file D. It is required

Today's 5 Reels (from the 90-Day Plan Excel)

126/450	Concept	open, read, write
127/450	Live demo	Notes app file mein save
128/450	Common mistake	Mode w file mita deta
129/450	Quiz	Quiz: lines count karo
130/450	Interview / real life	Real life: logs likhna

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