Python2代码在Python3运行报错：name 'onset_to_death' is not defined

Hey there! I totally get how frustrating it is when you’ve worked through most Python 2→3 compatibility issues for your EpiSkills course, only to hit this roadblock. Let’s break down why this error is happening and how to fix it.

First, let’s clarify: this error means Python can’t find any variable, function, or object named onset_to_death in your current environment. It’s usually tied to one of a few common issues, especially in a Jupyter Notebook context.

Possible Causes & Fixes #

1. You didn’t run the code that defines onset_to_death #

Jupyter Notebooks run cells in the order you execute them—not just the top-to-bottom order they’re displayed. If the cell that creates onset_to_death (from your course materials) was skipped, or you ran cells out of sequence, the variable never got created.

• Fix: Go back to your course’s instructions and locate the exact code block that defines onset_to_death. Make sure you run that cell first, and check that it finishes without errors. If that cell had a Python 2→3 compatibility bug (like using print as a statement instead of a function, or xrange instead of range), fix that first before re-running.

2. The definition code failed silently due to Python 2/3 differences #

Sometimes code that works in Python 2 might throw a subtle error in Python 3 that stops onset_to_death from being created, but you might have missed the error message.

• Common compatibility issues to check in the definition code:
  • If the code uses iteritems() on a dictionary, replace it with items() (Python 3’s items() behaves like Python 2’s iteritems()).
  • If it uses raw_input(), swap it for Python 3’s input().
  • If it reads files with open() without an encoding parameter, add encoding='utf-8' (e.g., open('data.csv', 'r', encoding='utf-8')).
  • If it uses unicode() to handle strings, replace it with str().

3. Scope or namespace issues #

It’s possible onset_to_death was defined inside a function or a different namespace, and you’re trying to access it outside that scope. Or maybe you accidentally cleared your notebook’s namespace (e.g., using %reset or restarting the kernel without re-running all cells).

• Fix:
  • Run the magic command %whos in a new cell to list all variables currently in your environment. If onset_to_death isn’t listed, you know the definition step failed.
  • If you restarted the kernel, re-run all cells from the top of the notebook to rebuild your environment.

4. Simple typo #

Double-check that you’re spelling onset_to_death exactly the same way it was defined. A tiny typo (like onset_to_deathh or onset_to_deat) will trigger this error every time.

Quick Debugging Step #

Add a cell right before the one that throws the error, and run this:

# Check if the variable exists
try:
    print(onset_to_death)
except NameError:
    print("onset_to_death is NOT defined—go back to its definition code!")

This will confirm whether the variable is missing, and point you straight to fixing the definition step.

内容的提问来源于stack exchange，提问作者arnold-c