NameError in class definition using list comprehension with if statement

[matesken]

This code works

class A:
    data = ' '
    remains = [c for c in data]

This code gives us NameError: name 'data' is not defined

class A:
    data = ' '
    remains = [c for c in data if c in data]

Is there any valid reason why this happens (running Python 3.9)?