Small Python bug fix

I am looking for a Python developer to fix a small bug in my code. The error message has been provided, but I am not sure about the current Python version being used. I need this bug fix urgently, so a quick turnaround time is required.

Ideal Skills and Experience:
- Strong proficiency in Python programming
- Experience in debugging and fixing Python code
- Familiarity with different Python versions (Python 2 and Python 3)
- Ability to work under tight deadlines and deliver high-quality results