Question 101 markMCQSection A

$Consider the statement given below : `` python f1 = open("pqr.dat","__") `` Which of the following is the correct file mode to open the file in read only mode ?$

Q: Consider the statement given below : ```python f1 = open("pqr.dat","________") ``` Which of the following is the correct file mode to open the file in read only mode ?

**Correct option: (B) rb** Since `pqr.dat` is a binary data file, it must be opened in binary mode; `rb` opens the file strictly for reading in binary mode, which is the correct read-only mode.

File Handling in Python

File Handling - File Opening Modes

Options

(A)

a

(B)

rb

(C)

r+

(D)

rb+

Official answer

Correct option: (B) rb Since pqr.dat is a binary data file, it must be opened in binary mode; rb opens the file strictly for reading in binary mode, which is the correct read-only mode.

file opening modes

binary file

read only mode

open() function

rb mode

file handling python

Marking scheme

1. $1 mark: correct option (B) rb selected.$

Hint

$Match the file mode to two things: text vs binary content, and whether writing should be possible.$

Quick oral answer

$rb opens a binary file strictly for reading; unlike r+ or rb+, it does not permit writing, making it the true read-only mode for a .dat file.$

Common mistakes

1. $Choosing r+ or rb+ thinking they are 'safer' read modes, without realizing the '+' allows writing too.$
2. $Forgetting that a .dat file needs binary mode (rb) rather than plain text mode (r).$

Analysis and explanation

File mode selection depends on both the intended operation (read/write) and the file's nature (text/binary). Why (B) is correct A .dat file conventionally stores binary data (such as pickled Python objects), so it should be opened in binary mode. rb stands for 'read binary' — it opens the file only for reading; if the file does not exist, Python raises a FileNotFoundError instead of creating one, confirming it is read-only. Why the other options are wrong (A) a opens the file for appending (writing at the end); it is not a read mode at all. (C) r+ opens the file for both reading and writing in text mode — it is not read-only. (D) rb+ opens the file for both reading and writing in binary mode — like r+, it allows writing, so it is not read-only.

Interesting facts

$Python's open() defaults to text mode ('rt') if no mode is specified, but binary files like .dat, images, or pickled objects must always be opened with a 'b' flag to avoid data corruption.$

$Opening a non-existent file in 'r' or 'rb' mode raises a FileNotFoundError, while 'a' or 'w' modes silently create the file if it doesn't exist.$

Question details

Q10 of 48 questions

Board: CBSE
Class: Class 12
Subject: Computer Science
Year: 2026
Section: Section A
Marks: 1
Type: MCQ
Chapter: File Handling in Python
Topic: $File Handling - File Opening Modes$
Bloom's level: remember
Syllabus topic: $Unit 1: Computational Thinking and Programming - 2 — File Handling: Binary File Access Modes$
Author: CBSE
Reviewed by: Padhantu Academic Team

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Frequently asked questions

$Why is 'r' not one of the options if it means read-only?$

$'r' is the default text-mode read-only flag, but since pqr.dat is a binary data file, plain text mode 'r' would misinterpret its bytes; the paper instead tests recognition that binary files need 'rb', the binary equivalent of read-only mode.$

$What is the difference between r+ and rb+?$

$r+ opens a file for both reading and writing in text mode, while rb+ does the same in binary mode. Both allow writing, so neither is a strictly read-only mode, unlike rb.$