What typical or noticeable errors have you found during code review?

During code review in Python, the following errors are often encountered:

• Code style violations (PEP8): incorrect indentation, overly long lines, uninformative variable names.
• Using mutable objects as default values in functions:

  def foo(data=[]):  # Bad
      data.append(1)
      return data
  

• Lack of exception handling or overly broad try-except blocks.
• Inefficient algorithms or excessive code complexity.
• Incorrect use of generators and iterators.
• Resource management issues, such as unclosed files or connections.
• Lack or insufficiency of comments and documentation, especially for complex logic.
• Use of outdated or insecure libraries and functions.

Detecting and fixing such errors improves code quality and maintainability.