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Python

Introduction to Python

Python Basics

Cotrol Structures

Data Structures

Date and Time

Functions and Module

File Handling

Python OOP

Advanced Concepts

Python DSA

Searching Algorithms

Sorting Algorithms

Python Read Files

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To read a file in Python, use the built-in open() function with read mode ("r").

f = open("demo.txt", "r")
print(f.read())
f.close()

🔹 read() – Read Entire File

f = open("demo.txt", "r")
print(f.read())
f.close()

✅ Reads all content of the file as a single string.

🔹 read(n) – Read Specific Characters

f = open("demo.txt", "r")
print(f.read(10))  # Reads first 10 characters
f.close()

🔹 readline() – Read One Line

f = open("demo.txt", "r")
print(f.readline())
f.close()

✅ Use it again to read the next line.

🔹 readlines() – Read All Lines into List

f = open("demo.txt", "r")
lines = f.readlines()
print(lines)
f.close()

✅ Each line becomes an item in the list.

🔹 Loop Through Lines

f = open("demo.txt", "r")
for line in f:
    print(line.strip())
f.close()

✅ Best way to read big files, one line at a time.

🔹 Use with Statement (Best Practice)

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

✅ Automatically closes the file after reading.

🔹 Read Binary File

with open("image.jpg", "rb") as file:
    data = file.read()

🔹 File Pointer Behavior

Each read() or readline() moves the pointer forward.

Practice Questions

Q1. Write a Python program to read and print all contents from sample.txt.

Q2. Write a Python program to read only the first 20 characters of a file using read(20).

Q3. Write a Python program to use readline() to read one line at a time from a file.

Q4. Write a Python program to loop through all lines in a file and print them using a for loop.

Q5. Write a Python program to read all lines using readlines() and print them as a list.

Q6. Write a Python program to strip newline characters when printing lines from a file.

Q7. Write a Python program to use with open() to safely read a file, ensuring it is properly closed.

Q8. Write a Python program to count the number of lines in a file using a loop.

Q9. Write a Python program to read a binary file (e.g., an image) using 'rb' mode and print its byte size.

Q10. Write a Python program to use read(0) on a file and explain the result (it returns an empty string because 0 characters were requested).

Python Read Files Quiz

Q1: What is the default mode of open()?

A. write
B. append
C. read
D. binary

Q2: What does read() return?

A. List
B. One line
C. Entire content as string
D. Dictionary

Q3: What does readline() return?

A. All lines
B. List
C. Next line as string
D. None

Q4: Which method returns all lines as a list?

A. read()
B. readline()
C. readlines()
D. openlines()

Q5: What is the use of with open()?

A. Creates file
B. Prevents read
C. Auto-closes file
D. Deletes file

Q6: What happens if file does not exist in read mode?

A. It is created
B. File is emptied
C. Error is raised
D. File is renamed

Q7: What does "rb" mode do?

A. Writes text
B. Reads binary
C. Appends string
D. Resets file

Q8: Which is more memory-efficient for large files?

A. read()
B. readlines()
C. read(1000000)
D. for line in file

Q9: What type is returned by f.read()?

A. int
B. str
C. list
D. bool

Q10: After read() is called, where is the pointer?

A. At start
B. At first character
C. At end
D. At middle
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