If Then statement

[nilamo]

1) df3 isn't defined, so you can't iterate over nothing.
2) NaN isn't defined, so you can't set X to it.
3) Even if both of those did exist, setting the temporary variable X to whatever NaN is wouldn't persist that change outside of the for-loop.

>>> items = [2, 5, 2, 4, 3, -32, 4]
>>> for item in items:
...   if item < 0:
...     item = None
...
>>> items
[2, 5, 2, 4, 3, -32, 4]