What common mistakes do developers make when writing code and how to avoid them?

Common mistakes when writing Python code and how to avoid them:

• Indentation errors: Python is sensitive to indentation; incorrect alignment leads to SyntaxError. Use a consistent style of indentation (spaces or tabs) and configure your editor.

• Modifying mutable default arguments in functions: Using mutable objects (like lists) as default values can lead to unexpected behavior. It's better to use None and create the object inside the function.

• Uncaught exceptions: Lack of error handling can cause the program to crash. Use try-except blocks to handle expected errors.

• Incorrect use of variables and scope: Confusion between local and global variables can cause errors. Watch the scope and use global or nonlocal when necessary.

• Poor variable naming: Unclear names make code harder to read. Use meaningful and descriptive names.

• Ignoring documentation and comments: Without comments and documentation, code becomes difficult to maintain.

• Suboptimal use of data structures: For example, using a list where a set or dictionary would be more appropriate.

To avoid errors, it is recommended to:

• Write tests
• Use static code analyzers (e.g., pylint, flake8)
• Follow PEP 8 — the official Python style guide
• Conduct code reviews

Example of an error with a mutable default argument:

def add_item(item, items=[]):
    items.append(item)
    return items

print(add_item(1))  # [1]
print(add_item(2))  # [1, 2] — unexpected!

Correct version:

def add_item(item, items=None):
    if items is None:
        items = []
    items.append(item)
    return items

print(add_item(1))  # [1]
print(add_item(2))  # [2]