What is the difference between NaN and None?

I am reading two columns of a csv file using pandas readcsv() and then assigning the values to a dictionary. The columns contain strings of numbers and letters. Occasionally there are cases where a cell is empty. In my opinion, the value read to that dictionary entry should be None but instead nan is assigned. Surely None is more descriptive of an empty cell as it has a null value, whereas nan just says that the value read is not a number.

How do I correctly clean up a Python object?

class Package: def __init__(self): self.files = [] # … def __del__(self): for file in self.files: os.unlink(file) __del__(self) above fails with an AttributeError exception. I understand Python doesn’t guarantee the existence of “global variables” (member data in this context?) when __del__() is invoked. If that is the case and this is the reason for the exception, … Read more