Python changing attribute mystery. Help?

[This article was first published on python – Win-Vector Blog, and kindly contributed to python-bloggers]. (You can report issue about the content on this page here)
Want to share your content on python-bloggers? click here.

Python peeps: any idea why this attribute changes value when I re-examine it? I am using PyCharm, but the calculation is weird even in Jupyter.

It doesn’t just seem to be the debugger, running it in Jupyter gives the wrong value (just {'x'}, instead of {'x', 'y'}). The type appears to be a dictionary object as an attribute of a class, but the field is acting strange.

The error is triggered here.

To leave a comment for the author, please follow the link and comment on their blog: python – Win-Vector Blog.

Want to share your content on python-bloggers? click here.