⚙️ Performance & Best Practices — Writing Better Code

Learn best practices for file operations to write safe, efficient code.

🎯 Best Practices

1. Always use `with` statement

# ✅ Good - file always closes
with open("data.txt", "r") as file:
    content = file.read()

# ❌ Bad - might not close if error occurs
file = open("data.txt", "r")
content = file.read()
file.close()

2. Check if file exists before reading

from pathlib import Path

path = Path("config.json")

# ✅ Good - check first
if path.exists():
    data = path.read_text()
else:
    print("File not found!")

# ❌ Bad - error if file missing
data = path.read_text()  # FileNotFoundError!

3. Use proper encoding

# ✅ Good - explicit encoding
with open("text.txt", "r", encoding="utf-8") as file:
    content = file.read()

# ❌ Bad - might fail on some systems
with open("text.txt", "r") as file:
    content = file.read()

💡 Performance Tips

Read Large Files Efficiently

# ❌ Bad - loads entire file into memory
with open("huge_file.txt", "r") as file:
    content = file.read()  # 1GB+ in memory!

# ✅ Good - process line by line
with open("huge_file.txt", "r") as file:
    for line in file:
        process(line)  # Process one line at a time

Use Buffering for Writes

# ✅ Good - single write operation
with open("output.txt", "w") as file:
    file.writelines(lines)  # All at once

# ❌ Bad - many write operations
with open("output.txt", "w") as file:
    for line in lines:
        file.write(line)  # Slow!

🎨 Common Patterns

Safe file copying

from pathlib import Path

def safe_copy(source, dest):
    """Copy file safely"""
    source = Path(source)
    dest = Path(dest)

    if not source.exists():
        raise FileNotFoundError(f"{source} not found")

    with open(source, "rb") as src, open(dest, "wb") as dst:
        dst.write(src.read())

Safe file writing (atomic)

from pathlib import Path
import tempfile

def safe_write(path, content):
    """Write file safely (atomic)"""
    path = Path(path)

    # Write to temp file first
    with tempfile.NamedTemporaryFile(
        mode="w", dir=path.parent, delete=False
    ) as tmp:
        tmp.write(content)
        tmp_path = tmp.name

    # Replace original atomically
    Path(tmp_path).replace(path)

📊 Checklist

• [ ] Always use `with` statement

• [ ] Check file exists before reading

• [ ] Use UTF-8 encoding explicitly

• [ ] Process large files line-by-line

• [ ] Batch writes for efficiency

• [ ] Handle exceptions gracefully

🔑 Key Takeaways

• ✅ `with` for automatic resource management

• ✅ `Path.exists()` before reading

• ✅ Explicit encoding (UTF-8)

• ✅ Line-by-line for large files

• ✅ Batch operations for performance

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