File modes and access types in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this code when reading a file?

Consider a file example.txt containing the text "Hello World". What will be printed by the following code?

Python

with open('example.txt', 'r') as f:
    content = f.read(5)
    print(content)

A "Hello World"

B "Hello\n"

C "Hello"

D "World"

💡 Hint

The read(n) method reads n characters from the file starting at the beginning.

The code reads only the first 5 characters from the file, which are "Hello". It does not read the entire file.

❓ Predict Output

intermediate

What happens when opening a file in 'w' mode?

Given a file data.txt that already contains some text, what will be the content of the file after running this code?

Python

with open('data.txt', 'w') as f:
    f.write('New content')

A The code will raise an error because the file exists.

B The file will contain the old content plus "New content" appended.

C The file will be unchanged.

D The file will contain "New content" only.

💡 Hint

Opening a file in 'w' mode clears its content before writing.

Mode 'w' opens the file for writing and truncates it to zero length, so old content is removed.

❓ Predict Output

advanced

What error does this code raise when opening a non-existent file?

What error will this code raise if missing.txt does not exist?

Python

with open('missing.txt', 'r') as f:
    data = f.read()

A FileNotFoundError

B PermissionError

C IsADirectoryError

D No error, file is created automatically

💡 Hint

Opening a file in read mode requires the file to exist.

Trying to open a non-existent file in 'r' mode raises FileNotFoundError.

❓ Predict Output

advanced

What is the content of the file after this code runs?

Assume log.txt initially contains "Start\n". What will be the content after running this code?

Python

with open('log.txt', 'a') as f:
    f.write('End\n')

A "End\n"

B "Start\nEnd\n"

C "Start\n"

D The file is empty

💡 Hint

Mode 'a' appends to the file without deleting existing content.

Opening in append mode adds new text at the end, so original content remains.

🧠 Conceptual

expert

Which file mode allows both reading and writing without truncating the file?

Choose the file mode that opens a file for both reading and writing, but does not erase the existing content when opened.

A "r+"

B "w+"

C "a+"

D "x+"

💡 Hint

One mode allows reading and writing and keeps existing content intact.

Mode r+ opens for reading and writing without truncating. w+ truncates, a+ appends, x+ creates new file only.

Practice

1. Which file mode in Python opens a file for reading only, and raises an error if the file does not exist?
file = open('data.txt', mode)

easy

A. "r"

B. "w"

C. "a"

D. "x"

Solution

1. Step 1: Understand the purpose of mode "r"

   Mode "r" opens a file for reading only and requires the file to exist.

2. Step 2: Compare with other modes

   Mode "w" opens for writing (creates or truncates), "a" appends, and "x" creates a new file but errors if it exists.

3. Final Answer:

   "r" -> Option A

4. Quick Check:

   Read-only mode = "r" [OK]

Hint: Read-only mode is just "r" [OK]

Common Mistakes:

• Confusing "r" with "w" which overwrites files
• Using "a" thinking it reads
• Choosing "x" which creates files

2. Which of the following is the correct syntax to open a file named log.txt for appending text in Python?

easy

A. open('log.txt', 'r')

B. open('log.txt', 'w')

C. open('log.txt', 'a')

D. open('log.txt', 'x')

Solution

1. Step 1: Identify the mode for appending

   Mode "a" opens the file for appending, adding new content at the end.

2. Step 2: Check syntax correctness

   The syntax open('log.txt', 'a') is correct for appending text.

3. Final Answer:

   open('log.txt', 'a') -> Option C

4. Quick Check:

   Append mode = "a" [OK]

Hint: Append mode is always "a" [OK]

Common Mistakes:

• Using "r" which is read-only
• Using "w" which overwrites the file
• Using "x" which creates new file only

3. What will be the output of the following code if example.txt contains the text "Hello"?

with open('example.txt', 'w') as f:
    f.write('World')

with open('example.txt', 'r') as f:
    print(f.read())

medium

A. World

B. Hello

C. HelloWorld

D. Error

Solution

1. Step 1: Understand mode "w" effect on file content

   Opening with "w" overwrites the file, so "World" replaces "Hello".

2. Step 2: Reading the file after writing

   Reading the file after writing will output the new content "World".

3. Final Answer:

   World -> Option A

4. Quick Check:

   Write mode overwrites content = "World" [OK]

Hint: Write mode "w" replaces file content [OK]

Common Mistakes:

• Assuming "w" appends instead of overwrites
• Expecting original content to remain
• Thinking reading causes error after writing

4. What is wrong with this code snippet?

f = open('data.txt', 'r')
content = f.read()
f.write('More data')
f.close()

medium

A. No error, code is correct

B. File is not closed properly

C. File mode should be "a" to read

D. File is opened in read mode but write is attempted

Solution

1. Step 1: Check file mode and operations

   The file is opened in "r" (read) mode, which does not allow writing.

2. Step 2: Identify the error cause

   Calling f.write() in read mode causes a runtime error because writing is not allowed.

3. Final Answer:

   File is opened in read mode but write is attempted -> Option D

4. Quick Check:

   Write not allowed in "r" mode [OK]

Hint: Write needs "w" or "a" mode, not "r" [OK]

Common Mistakes:

• Forgetting write is disallowed in read mode
• Not closing file properly (though here it is closed)
• Confusing append mode with read mode

5. You want to create a new file report.txt but only if it does not already exist. Which mode should you use to avoid overwriting existing files?

hard

A. "w"

B. "x"

C. "a"

D. "r+"

Solution

1. Step 1: Understand mode "x" behavior

   Mode "x" creates a new file and raises an error if the file already exists, preventing overwriting.

2. Step 2: Compare with other modes

   "w" overwrites, "a" appends or creates, "r+" opens for reading and writing but requires file to exist.

3. Final Answer:

   "x" -> Option B

4. Quick Check:

   Create new only = "x" mode [OK]

Hint: Use "x" to create file only if not exists [OK]

Common Mistakes:

• Using "w" which overwrites existing files
• Using "a" which appends or creates silently
• Using "r+" which needs existing file