File modes and access types in Python - Mini Project: Build & Apply

File modes and access types

📖 Scenario: You are working on a simple program that saves and reads notes from a text file. You will learn how to open files in different modes to write and read data.

🎯 Goal: Build a program that creates a file, writes a note, reads the note back, and shows the content on the screen using correct file modes.

📋 What You'll Learn

Create a file and write text to it using the correct file mode

Open the file to read the text back

Use the correct file modes for writing and reading

Print the content read from the file

💡 Why This Matters

🌍 Real World

Saving and reading notes or logs is common in many apps like diaries, to-do lists, or data logging.

💼 Career

Understanding file modes is essential for jobs involving data processing, automation, and software development.

1

Create and open a file in write mode

Create a variable called file and open a file named notes.txt in write mode using open('notes.txt', 'w').

Python

# Create a variable called file and open 'notes.txt' in write mode
# Your code here

Hint

Use 'w' mode to open a file for writing. This will create the file if it does not exist.

2

Write a note to the file

Use the write method on the file variable to write the string 'My first note.' to the file.

Python

file = open('notes.txt', 'w')
# Write 'My first note.' to the file
# Your code here

Hint

Use file.write('My first note.') to add text to the file.

3

Close the file and reopen in read mode

Close the file using file.close(). Then create a new variable called file and open notes.txt in read mode using open('notes.txt', 'r').

Python

file = open('notes.txt', 'w')
file.write('My first note.')
# Close the file
# Reopen the file in read mode
# Your code here

Hint

Always close a file after writing. Use file.close(). Then open it again with 'r' mode to read.

4

Read and print the file content

Read the content of the file using file.read() and print it using print(). Then close the file.

Python

file = open('notes.txt', 'w')
file.write('My first note.')
file.close()
file = open('notes.txt', 'r')
# Read the content and print it
# Close the file
# Your code here

Hint

Use content = file.read() to get the text, then print(content) to show it.

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