How to “negate” value: if true return false, if false return true?

Use the not boolean operator:

nyval = not myval

not returns a boolean value (True or False):

>>> not 1
False
>>> not 0
True

If you must have an integer, cast it back:

nyval = int(not myval)

However, the python bool type is a subclass of int, so this may not be needed:

>>> int(not 0)
1
>>> int(not 1)
0
>>> not 0 == 1
True
>>> not 1 == 0
True