File I/O

# Basic open/close
file = open("data.txt", "r")
content = file.read()
file.close()

# Context manager — auto-closes even on errors
with open("data.txt", "r") as file:
    content = file.read()

# Modes:
# "r"  — read (default)
# "w"  — write (overwrites existing)
# "a"  — append
# "x"  — exclusive creation (fails if exists)
# "b"  — binary mode
# "t"  — text mode (default)
# "+"  — read and write

with open("notes.txt", "w") as f:
    f.write("New content")       # Overwrites

with open("notes.txt", "a") as f:
    f.write("\nMore content")    # Appends

with open("new_file.txt", "x") as f:
    f.write("Created")           # Fails if exists

with open("data.txt", "r") as f:
    # All at once
    content = f.read()           # Entire file as string

    # Line by line
    for line in f:               # Memory efficient for large files
        print(line.strip())

    # All lines
    lines = f.readlines()        # List of strings
    lines = f.read().splitlines()  # Without trailing newlines

    # Read specific amount
    chunk = f.read(1024)         # First 1024 bytes

# Text files
with open("output.txt", "w", encoding="utf-8") as f:
    f.write("Line 1\n")
    f.write("Line 2\n")
    f.writelines(["Line 3\n", "Line 4\n"])

# Appending
with open("log.txt", "a") as f:
    print("Error occurred", file=f)  # print() can write to files

# Old way — string concatenation (brittle)
path = "/home/user/data/" + filename

# Better — pathlib (Python 3.4+)
from pathlib import Path

data_dir = Path("/home/user/data")
file_path = data_dir / "results.csv"  # Uses / operator

# Common operations
p = Path("data/config.json")

p.exists()          # True/False
p.is_file()         # True/False
p.is_dir()          # True/False
p.name              # 'config.json'
p.stem              # 'config'
p.suffix            # '.json'
p.parent            # Path('data')
p.absolute()        # Full path

# Reading/writing with pathlib
p.write_text('{"key": "value"}')
content = p.read_text()

# Directory operations
for item in Path(".").iterdir():
    print(item.name)

for py_file in Path("src").glob("**/*.py"):
    print(py_file)

# Create directories
Path("output/data").mkdir(parents=True, exist_ok=True)

# Reading binary
with open("image.jpg", "rb") as f:
    data = f.read()
    print(f"Read {len(data)} bytes")

# Writing binary
with open("output.bin", "wb") as f:
    f.write(b"\x00\x01\x02\x03")

# Copying binary
with open("source.jpg", "rb") as src, open("copy.jpg", "wb") as dst:
    dst.write(src.read())

from tempfile import TemporaryFile, NamedTemporaryFile, TemporaryDirectory

# Temporary file (no name, auto-deleted)
with TemporaryFile("w+") as f:
    f.write("Temporary data")
    f.seek(0)
    print(f.read())

# Named temporary file
with NamedTemporaryFile(delete=True) as f:
    print(f"Temp file: {f.name}")
    f.write(b"data")

# Temporary directory
with TemporaryDirectory() as tmpdir:
    path = Path(tmpdir) / "work.txt"
    path.write_text("Working here")

import csv

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

# Writing
with open("output.csv", "w", newline="") as f:
    writer = csv.DictWriter(f, fieldnames=["name", "age"])
    writer.writeheader()
    writer.writerow({"name": "Alice", "age": 30})

import json

data = {"users": [{"name": "Alice", "age": 30}]}

# Writing
with open("data.json", "w") as f:
    json.dump(data, f, indent=2)

# Reading
with open("data.json", "r") as f:
    loaded = json.load(f)

# String conversions
json_str = json.dumps(data)
parsed = json.loads(json_str)

import shutil
import os

# Copy
shutil.copy("source.txt", "dest.txt")           # File
shutil.copytree("src_dir", "dest_dir")           # Directory

# Move/Rename
shutil.move("old.txt", "new.txt")

# Delete
os.remove("file.txt")                            # File
os.rmdir("empty_dir")                            # Empty directory
shutil.rmtree("dir_to_delete")                   # Directory + contents

# File info
os.path.getsize("data.txt")                      # Size in bytes
os.path.getmtime("data.txt")                     # Last modified timestamp