Variables in debug mode

I have a function that uses a global variable, 'c', as part of a SQL query (although I'm assuming the fact it's part of a SQL query is not important):

def myfunc(a, b):

       df = pd.read_sql('select * from {var}'.format(var=c))

       ...

when in debug mode I can't access c, it's not available to me. As a workaround, I tried to define c using both the debugger prompt and the 'evaluate' function; this *looks like* it works; i.e. 'c' appears in my varibable list; but the debugger doesn't recognise it.

So, how can I define/access my 'c' variable?

Cheers,

Graham