How to get defined local variable to combobox as values in python?

Question

I am working on a project where I required defined function variable(local variable) in the values of Combobox but it gives me error of undefined variable. And I cannot change the pattern of my python script otherwise the script will mixed up and gives other error.

Please help me to solve the problem without changing the script pattern.

Here is my code:-

book= ''
pages = 1
page_no = 1
pdfReader=''
def selectBtnClicked():
    # pass
    global book
    global PDFFILE
    global pages
    global page_no
    global pdfReader
    print(PDFFILE)
    # PDFFILE1=pdf_btnClicked()
    book = open(PDFFILE, 'rb')
    pdfReader = PyPDF2.PdfFileReader(book)
    pages = pdfReader.numPages
    print(pages)
    pages += 1
    page_no = [i for i in range(1, pages)]
    print(page_no)
    return page_no, pdfReader

#start from
style = ttk.Style()
style.theme_use("default")
style.map('TCombobox', fieldbackground=[('readonly','red')])
style.map('TCombobox', selectbackground=[('readonly', 'red')])
style.map('TCombobox', selectforeground=[('readonly', 'white')])
n= tk.StringVar(value="---STARTING PAGE---")
n.set("---STARTING PAGE---")
startfromLabel = ttk.Combobox(root, font=font, justify='center', textvariable=n)
startfromLabel["values"]= page_no
# pages_nos()
startfromLabel["state"] = "readonly"
startfromLabel.bind('<<ComboboxSelected>>')
startfromLabel.current()
startfromLabel["foreground"] = '#ffffff'
startfromLabel.pack(side=TOP, pady=30)
  
root.mainloop()

I need page_no as value of startfromLabel but I am not getting the values in my GUI output:

Answer 1

Your not telling to change the values inside the function, so say:

def selectBtnClicked():
    .... #same bunch of code
 
    startfromLabel["values"] = page_no
    .... #remaining bunch of code