Writing file data in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this file write operation?

Consider this Python code that writes to a file and then reads it back. What will be printed?

Python

with open('testfile.txt', 'w') as f:
    f.write('Hello\nWorld')

with open('testfile.txt', 'r') as f:
    content = f.read()
print(content)

A

Hello
World

B Hello World

C Hello\nWorld

D SyntaxError

💡 Hint

Remember that '\n' is a newline character in strings.

The write method writes the string with a newline character, so when reading back, the content has two lines: 'Hello' and 'World'.

❓ Predict Output

intermediate

What happens if you write to a file opened in append mode?

Given this code, what will be the content of 'append.txt' after running it twice?

Python

with open('append.txt', 'a') as f:
    f.write('Line\n')

A The file will contain 'Line\nLine\n'

B The file will contain only 'Line\n'

C The file will be overwritten with 'Line\n'

D Raises an error because 'a' mode does not allow writing

💡 Hint

Append mode adds data to the end of the file without deleting existing content.

Opening a file in append mode ('a') adds new data to the end. Running twice adds two lines.

❓ Predict Output

advanced

What is the output of this code that writes and reads binary data?

Look at this Python code that writes bytes to a file and then reads it back. What will be printed?

Python

data = b'\x48\x65\x6c\x6c\x6f'
with open('binary.dat', 'wb') as f:
    f.write(data)

with open('binary.dat', 'rb') as f:
    content = f.read()
print(content)

A b'\x48\x65\x6c\x6c\x6f'

B 'Hello'

C b'Hello'

D UnicodeDecodeError

💡 Hint

Binary mode reads and writes bytes, so the output is a bytes object.

The bytes written are the ASCII codes for 'Hello'. Reading in binary mode returns the same bytes object.

❓ Predict Output

advanced

What error does this code raise when writing to a file opened in read mode?

What happens when you try to write to a file opened with mode 'r'?

Python

with open('file.txt', 'r') as f:
    f.write('Test')

A FileNotFoundError

B io.UnsupportedOperation: not writable

C TypeError

D No error, writes successfully

💡 Hint

Files opened in read mode do not allow writing.

Trying to write to a file opened in 'r' mode raises an io.UnsupportedOperation error because the file is not writable.

🧠 Conceptual

expert

How many lines will be in the file after running this code?

This code writes lines to a file inside a loop. How many lines will the file contain after running it once?

Python

with open('lines.txt', 'w') as f:
    for i in range(5):
        f.write(f'Line {i}\n')
    f.write('End')

A 5

B 7

C 4

D 6

💡 Hint

Count the lines written including the last write without a newline.

The loop writes 5 lines each ending with a newline, then one more line 'End' without newline, so total lines are 6.