🌱 Junior Track 13 of 13

13. File Handling & pathlib

Work with files cleanly: `open()`, context managers (`with`), reading/writing/appending, text vs. binary modes, file paths, and modern `pathlib.Path` operations.

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1️⃣ Fundamentals 2️⃣ Data Types 3️⃣ Operators 4️⃣ Conditionals 5️⃣ Loops 6️⃣ Collections 7️⃣ Comprehensions 8️⃣ Functions 9️⃣ *args & **kwargs 🔟 Scope & Namespaces 1️⃣1️⃣ OOP 1️⃣2️⃣ Exceptions 1️⃣3️⃣ File Handling 1️⃣4️⃣ Modules & Packages 1️⃣5️⃣ Virtual Environments 1️⃣6️⃣ Standard Library 1️⃣7️⃣ Iterators & Iterables 1️⃣8️⃣ Generators 1️⃣9️⃣ Decorators 2️⃣0️⃣ Context Managers 2️⃣1️⃣ Lambda Functions 2️⃣2️⃣ Functional Programming 2️⃣3️⃣ Type Hints 2️⃣4️⃣ Dataclasses 2️⃣5️⃣ Testing 2️⃣6️⃣ Debugging 2️⃣7️⃣ Logging 2️⃣8️⃣ JSON & Data 2️⃣9️⃣ Regular Expressions 3️⃣0️⃣ Databases

# ==============================================================================
# JUNIOR PYTHON TRACK 13 — FILE HANDLING & PATHLIB
# ==============================================================================

from pathlib import Path

# 1. Writing Text File using Context Manager ('w' mode)
file_path = Path("demo_notes.txt")

with open(file_path, mode="w", encoding="utf-8") as file:
    file.write("Line 1: Python Masterclass\n")
    file.write("Line 2: Context Managers close files automatically!\n")

# 2. Appending Lines ('a' mode)
with open(file_path, mode="a", encoding="utf-8") as file:
    file.write("Line 3: Appended content successfully.\n")

# 3. Reading Text File ('r' mode)
with open(file_path, mode="r", encoding="utf-8") as file:
    content = file.read()
    print("--- File Content via open() ---")
    print(content)

# 4. Modern pathlib.Path Operations
path_obj = Path("pathlib_demo.txt")
path_obj.write_text("Clean & elegant file I/O with pathlib!", encoding="utf-8")

if path_obj.exists():
    text = path_obj.read_text(encoding="utf-8")
    print(f"[PATHLIB READ] {text}")
    print(f"[INFO] File size: {path_obj.stat().st_size} bytes")

# 5. Writing and Reading Binary Files ('wb' / 'rb')
bin_path = Path("data.bin")
binary_payload = b"\x00\x01\x02\xFF\xFE"

with open(bin_path, mode="wb") as bfile:
    bfile.write(binary_payload)

with open(bin_path, mode="rb") as bfile:
    data = bfile.read()
    print(f"[BINARY READ] {data}")

# Cleanup generated demo files
file_path.unlink()
path_obj.unlink()
bin_path.unlink()

$ python3 junior_files.py
--- File Content via open() ---
Line 1: Python Masterclass
Line 2: Context Managers close files automatically!
Line 3: Appended content successfully.

[PATHLIB READ] Clean & elegant file I/O with pathlib!
[INFO] File size: 40 bytes
[BINARY READ] b'\x00\x01\x02\xff\xfe'
File cleanup finished.

import unittest
from pathlib import Path

class TestJuniorFileHandling(unittest.TestCase):
    def test_context_manager_write_read(self):
        p = Path("test_temp.txt")
        with open(p, "w", encoding="utf-8") as f:
            f.write("Hello World")
        
        self.assertTrue(p.exists())
        self.assertEqual(p.read_text(encoding="utf-8"), "Hello World")
        p.unlink()

if __name__ == "__main__":
    unittest.main()

🌱 Junior Track 13 Master Reference

13. Python File Handling & pathlib Reference

1️⃣ File Open Modes Cheat Sheet

Mode	Description	Behavior if File Exists	Behavior if File Missing
'r'	Read text (default).	Reads from start.	Raises FileNotFoundError.
'w'	Write text.	Truncates / overwrites file.	Creates new empty file.
'a'	Append text.	Appends data to end.	Creates new file.
'rb' / 'wb'	Binary Read / Write.	Processes raw bytes.	Same as text modes.

2️⃣ Reading Methods (`read`, `readline`, `readlines`)

file.read(): Reads the entire file content as a single string.
file.readline(): Reads a single line up to the newline \n character.
file.readlines(): Reads all lines and returns a Python list of strings.
for line in file:: Most memory-efficient way to iterate through large files line by line.

3️⃣ Modern Path Handling with `pathlib.Path`

                    from pathlib import Path

                    p = Path("logs/app.log")

                    p.parent.mkdir(parents=True, exist_ok=True)

                    p.write_text("[INFO] Server started successfully", encoding="utf-8")

                    content = p.read_text(encoding="utf-8")

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