Open, read, write and close files

Opening Files

Think of a file as a diary 📓. To read or write, you first open it, just like opening a diary to start writing.

file = open('data.txt', 'r')  # 'r' = read mode
file = open('data.txt', 'w')  # 'w' = write mode (overwrites)
file = open('data.txt', 'a')  # 'a' = append mode (adds to end)
  

• Use 'r' for reading only.
• Use 'w' to create a new file or overwrite.
• Use 'a' to add new content without deleting existing data.

Reading Files

Once the diary is open, you can read its contents. Python offers several ways:

1. Read the whole file:

   content = file.read()
         

2. Read line by line:

   for line in file:
       print(line.strip())
         

3. Read all lines into a list:

   lines = file.readlines()
         

Remember: Always close the file after reading.

Writing Files

Writing is like adding new entries to your diary. Use the following pattern:

with open('data.txt', 'w') as file:
    file.write('Hello, world!\')
    file.write('Second line.')
  

Using with automatically closes the file, but if you open it manually, you must close it yourself.

Closing Files

Just as you close a diary after writing, you must close a file to free resources:

file.close()
  

Or use with for automatic closing:

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

Common Errors & How to Avoid Them

• FileNotFoundError: Trying to read a file that doesn't exist. Use try/except or check with os.path.exists().
• PermissionError: Trying to write to a read‑only location. Ensure you have write permissions.
• Unclosed File: Leaving a file open can lock it. Use with or remember to call close().

Exam Tips

When answering exam questions about file handling, keep these points in mind:

1. Show the correct mode for the task (e.g., 'r' for reading, 'w' for writing).
2. Include the file path (relative or absolute) and explain why it matters.
3. Demonstrate reading or writing with code snippets.
4. Explain the importance of closing the file or using with.
5. Use an analogy (like a diary) to show understanding.

Good luck! 🚀