File I/O

# Read entire file
with open("data.txt", "r") as f:
    content = f.read()
    print(content)

# Read line by line
with open("data.txt", "r") as f:
    for line in f:
        print(line.strip())

# Read single line
with open("data.txt", "r") as f:
    first_line = f.readline()

# Read all lines into a list
with open("data.txt", "r") as f:
    lines = f.readlines()  # List of strings

# Write (creates or overwrites)
with open("output.txt", "w") as f:
    f.write("Hello, World!\n")
    f.write("Second line.\n")

# Append (adds to existing file)
with open("output.txt", "a") as f:
    f.write("Appended line.\n")

# Write multiple lines
lines = ["Line 1\n", "Line 2\n", "Line 3\n"]
with open("output.txt", "w") as f:
    f.writelines(lines)

import csv

# Reading CSV
with open("data.csv", "r") as f:
    reader = csv.reader(f)
    header = next(reader)  # Skip header row
    for row in reader:
        print(row)  # Each row is a list

# Reading CSV as dictionaries
with open("data.csv", "r") as f:
    reader = csv.DictReader(f)
    for row in reader:
        print(row["name"], row["age"])

# Writing CSV
with open("output.csv", "w", newline="") as f:
    writer = csv.writer(f)
    writer.writerow(["name", "age", "city"])
    writer.writerow(["Alice", 30, "NYC"])
    writer.writerow(["Bob", 25, "LA"])

import json

# Reading JSON
with open("data.json", "r") as f:
    data = json.load(f)
    print(data["name"])

# Writing JSON
data = {"name": "Alice", "scores": [95, 87, 92]}
with open("output.json", "w") as f:
    json.dump(data, f, indent=2)

# Convert between JSON strings and Python objects
json_str = json.dumps(data)           # Dict to JSON string
parsed = json.loads(json_str)          # JSON string to dict

try:
    with open("missing.txt", "r") as f:
        content = f.read()
except FileNotFoundError:
    print("File not found!")
except PermissionError:
    print("No permission to read file!")
except Exception as e:
    print(f"Unexpected error: {e}")
else:
    print("File read successfully!")
finally:
    print("This always runs.")

# Raising exceptions
def divide(a, b):
    if b == 0:
        raise ValueError("Cannot divide by zero!")
    return a / b

import os
from pathlib import Path

# Check if file exists
print(os.path.exists("data.txt"))
print(Path("data.txt").exists())

# Get file size
size = os.path.getsize("data.txt")

# List directory contents
files = os.listdir(".")

# Create directories
os.makedirs("output/subdir", exist_ok=True)

# Modern pathlib approach
p = Path("data") / "output.txt"
p.parent.mkdir(parents=True, exist_ok=True)
p.write_text("Hello from pathlib!")
content = p.read_text()