Working with Files and Directories

# ===== PATHLIB: MODERN FILE PATH HANDLING =====
from pathlib import Path

# Create path objects (cross-platform)
log_file = Path("/var/log/app.log")
config_dir = Path("/etc/myapp")

# Path operations
filename = log_file.name           # "app.log"
parent_dir = log_file.parent       # Path("/var/log")
stem = log_file.stem              # "app" (without .log)
suffix = log_file.suffix          # ".log"

# Check if path exists
if log_file.exists():
    print("Log file found")

if log_file.is_file():
    print("It is a file")

if log_file.parent.is_dir():
    print("Parent is a directory")

# ===== READING FILES =====
# Read entire file
with open("/var/log/app.log", "r") as file:
    content = file.read()
    print(content)

# Read line by line (memory-efficient for large files)
with open("/var/log/app.log", "r") as file:
    for line in file:
        line = line.rstrip("\n")    # remove newline
        if "ERROR" in line:
            print(f"Error found: {line}")

# Read all lines into list
with open("/var/log/app.log", "r") as file:
    lines = file.readlines()       # includes newlines
    lines = [l.strip() for l in lines]  # remove whitespace

# ===== WRITING FILES =====
# Write (overwrites if exists)
output_file = Path("report.txt")
with open(output_file, "w") as file:
    file.write("Report Header\n")
    file.write("==============\n")
    file.write("Data here\n")

# Append to file
with open(output_file, "a") as file:
    file.write("New line appended\n")

# Write multiple lines
lines = ["Line 1", "Line 2", "Line 3"]
with open(output_file, "w") as file:
    file.writelines([f"{line}\n" for line in lines])

# ===== LISTING FILES =====
# All files in directory
log_dir = Path("/var/log")
all_files = log_dir.iterdir()       # generator of all items
for item in all_files:
    print(item)

# List only files (not directories)
files = [f for f in log_dir.iterdir() if f.is_file()]

# Find files by pattern
log_files = log_dir.glob("*.log")   # all .log files in dir
all_logs = log_dir.rglob("*.log")   # .log files recursively

# ===== CREATING/DELETING DIRECTORIES =====
new_dir = Path("/tmp/myapp")
new_dir.mkdir(parents=True, exist_ok=True)  # create with parents

# Create file (touch)
new_file = new_dir / "data.txt"
new_file.touch()

# Remove file
new_file.unlink()

# Delete directory (if empty)
new_dir.rmdir()

# ===== WORKING WITH PERMISSIONS =====
# Check file permissions
stat_info = log_file.stat()
mode = stat_info.st_mode           # raw mode
size = stat_info.st_size           # file size in bytes
mtime = stat_info.st_mtime         # modification time

# ===== SAFE FILE READING: HANDLING ERRORS =====
def safe_read_log(filepath):
    """Read log file, handling common errors."""
    try:
        with open(filepath, "r") as f:
            return f.read()
    except FileNotFoundError:
        print(f"File not found: {filepath}")
        return None
    except PermissionError:
        print(f"Permission denied: {filepath}")
        return None
    except Exception as e:
        print(f"Error reading file: {e}")
        return None

# ===== PARSING STRUCTURED FILE DATA =====
# Read CSV-like data
def parse_csv_log(filepath):
    """Parse comma-separated log file."""
    data = []
    try:
        with open(filepath, "r") as f:
            for line in f:
                parts = line.strip().split(",")
                if len(parts) >= 3:
                    data.append({
                        "timestamp": parts[0],
                        "level": parts[1],
                        "message": parts[2]
                    })
    except Exception as e:
        print(f"Error parsing: {e}")
    return data

# ===== TEMPORARY FILES =====
import tempfile

# Create temporary file
with tempfile.NamedTemporaryFile(mode="w", delete=False) as tmp:
    tmp.write("temporary data")
    tmp_path = tmp.name

# Use the file
with open(tmp_path, "r") as f:
    content = f.read()

# Clean up (optional—usually auto-deleted)
Path(tmp_path).unlink()