Unresolved Reference in Python which is an integer

Question

When I write the following code:

def demorgan(prop_sent, conditionals, candd):

    global sn
    d = 0
    while d < len(conditionals) -1:
        str1 = conditionals[d][4]
        if str1.find("~(") > -1:
            anc1 = conditionals[d][2]

The IDE says that d is an unresolved reference. When I change the while loop to a for loop, which I can't do by the way, since the length of the conditionals list will change while looping, the error message goes away.

def demorgan(prop_sent, conditionals, candd):

    global sn

    for d in range(len(conditionals)):
        str1 = conditionals[d][4]
        if str1.find("~(") > -1:
            anc1 = conditionals[d][2]

I can't figure out why d is an unresolved reference in the while loop. The bug also goes away when I simply put in:

while d < 10:

Answer 1

Actually, on second thought this is not an error. My IDE editor (Pycharm) underlines the d variable and has a red flag in the right hand side, but when I actually step over the line, Python continues to work. This is the only time I've seen when a red flag has gone up and Python has continued to work, so I guess the problem is with the IDE.