Tkinter Command Lambda Function Modify Variable

Question

My application is a form which populates its fields from a database. I am in the process of writing the function that navigates between these records. I am having problems writing my "next record" function.

At any given time, the "Current Record" showing on the screen is in a variable current_record.

def next_record(current_record):
    current_index = current_record.index
    current_record = Competitor(competitors[current_index + 1], current_index + 1)
    print(current_record.index)
    populate_form(current_record)

And my button calling this function:

action_button_6 = tkinter.Button(group_buttons, text='>>', width=5,
                                 command=lambda: next_record(current_record))

Although the function does its job and loads the new record into the form, it does not reassign "current_record" to the new competitor as show in the third line of the function.

How can I modify the variable from within this function?

current_record in next_record is local variable and it have nothing to do with current_record in lambda. If you assign new element to current_record in next_record you lose contact with original record. — furas
– furas, Commented Nov 28, 2015 at 15:17
I know I have made life a little bit more difficult for myself by naming them all the same. My question is how can I modify the variable passed to the function in lambda? — ggle
– ggle, Commented Nov 28, 2015 at 15:18
You have to change valued in existing element if you can - like current_record.some_variable = competitors[current_index + 1] and current_record.index = current_index + 1. — furas
– furas, Commented Nov 28, 2015 at 15:20
so change the index of the current instance and then execute some internal class function to re-initialise? — ggle
– ggle, Commented Nov 28, 2015 at 15:22

Perry · Accepted Answer · 2015-11-28 15:49:16Z

0

Unless you explicitly declare a variable that you modify in a function global, it defaults to being local even if there is a global variable with the same name, thus current_record is a local variable. Adding global current_record to the beginning of the next_record function and renaming the function argument to old_record would fix that.

answered Nov 28, 2015 at 15:49

Perry

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