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📂 07_File_IO

Welcome to the File Input and Output (File I/O) section!
In this section, you’ll learn how Python interacts with files — reading data, writing new content, appending text, and using the with statement for efficient and safe file handling.

File handling is essential for real projects because it lets your programs store, retrieve, and process data persistently.

📘 Overview

Here you’ll explore:

  • How to open and close files properly.
  • File modes: read (r), write (w), append (a) (and notes about x, t, b).
  • Reading data using read(), readline(), and readlines().
  • Writing (overwrite) and appending (add) operations.
  • Using the with statement (context manager) to automatically close files.

📂 07_File_IO


07_File_IO/
│
├── 01_file_basics.py
├── 02_read_file.py
├── 03_write_file.py
├── 04_append_file.py
├── 06_with_statement.py
├── file.txt
├── poem.txt
├── word_search_in_file.py
└── README.md

🧩 Files Description

File Name Description
01_file_basics.py Intro to file handling: open(), close(), basic read() example and explanation of file modes.
02_read_file.py Demonstrates read(), readline() and readlines(). Shows reading with loops and .strip() to clean newline characters.
03_write_file.py Shows how to write to a file with mode "w" (overwrites existing content).
04_append_file.py Demonstrates appending text to an existing file using mode "a" (preserves existing content).
06_with_statement.py Explains and demonstrates with open(...) as f: — best practice for auto-closing files and safe handling.
file.txt, poem.txt Example data files used by the above scripts.

🧠 Example Code Snippets

Read whole file (basic)

# 01_file_basics.py (snippet)
f = open('file.txt', 'r')
content = f.read()
print(content)
f.close()

Read line-by-line and readlines()

# 02_read_file.py (snippet)
with open('file.txt', 'r') as f:
    lines = f.readlines()   # returns a list of lines
    for line in lines:
        print(line.strip())

Write (overwrite) a file

# 03_write_file.py (snippet)
st = 'A thing of beauty is a joy forever!'
with open('myfile.txt', 'w') as f:
    f.write(st)

Append to a file

# 04_append_file.py (snippet)
st = "\n(Author: John Keats)"
with open('myfile.txt', 'a') as f:
    f.write(st)

Using with (context manager)

# 06_with_statement.py (snippet)
with open('file.txt', 'r') as f:
    print(f.read())
# file auto-closed here

🎯 Learning Goals

By the end of this section you should be able to:

  • Explain and use the main file modes (r, w, a) and know when to use each.
  • Read files fully or line-by-line and process the content.
  • Write and append text files safely.
  • Use with open() to manage files without explicit close() calls.
  • Implement small file-based utilities (counters, mergers, cleaners).

✅ Tips & Best Practices

  • Prefer with open(...) for file operations — it’s safer and cleaner.
  • Use .strip() when printing lines to avoid extra blank lines.
  • Never hard-code absolute file paths if you plan to share the repo — use relative paths.
  • Avoid storing secrets or credentials in plain text files in the repo.

Next Section → 08_Exceptions_Debugging