user interface - Global name v is not defined (but it actually is)? tkinter/python -

i keep getting error "global name v not defined." know has been heavily documented, none of other threads relavant gui situation. anyway, here go:

v_amount= 5000  def set_v_to_something_else():     global v     v_amount=v_amount-1000     v.set(v_amount)  v = stringvar() v.set(str(v_amount))  #create button allow v label set else  vbutton = button(root, text = "change v", command = set_v_to_something_else).pack() vlabel = label(root, textvariable=v).pack() 

once again, says v not defined, though set equal stringvar()

thanks in advance

perhaps getting error

global name v_amount not defined 

that because, in code,

v_amount= 5000  def set_v_to_something_else():     global v     v_amount=v_amount-1000     v.set(v_amount) 

when python parses function set_v_to_something_else, marks v_amount local variable because appears on left-hand side of assignment:

v_amount=v_amount-1000 

later, when function called, since python regards v_amount local variable, tries evaluate right-hand side of assignment statement first , finds v_amount not defined. (remember, looking in local namespace, not global namespace.)

the fix add global v_amount inside function:

def set_v_to_something_else():     global v_amount     v_amount = v_amount-1000     v.set(v_amount) 

you can remove

global v 

because not assigning new value v. v.set merely calling method of v.