我正在开发一个应用程序，能够列出客户与开放收费的pdf格式。代码包括输入电子表格、检查尚未付款的客户并将其保存在字典中，然后将其保存为pdf。现在的情况是，它只列出了一个客户的pdf格式。
代码如下：

# !/usr/bin/env python

# -*- coding: utf-8 -*-

from __future__ import unicode_literals

from tkinter import *
from tkinter import ttk
from tkinter import messagebox
from reportlab.pdfgen import canvas
from reportlab.lib.pagesizes import A4
import openpyxl
import os

pastaApp = os.path.dirname(__file__)

def createPDF():
    # Opens the spreadsheet and obtains the status of the last payment.

    wb = openpyxl.load_workbook('C:/temp/cobranca.xlsx')
    sheet = wb['Sheet1']

    lastCol = sheet.max_column

    # Checks the payment status of each customer.

    unpaidMembers = {}
    clients = []
    months = []
    emails = []
    for r in range(2, sheet.max_row + 1):
        for c in range(3, lastCol + 1):
            payment = sheet.cell(row=r, column=c).value
            if payment != 'ok':
                client = sheet.cell(row=r, column=1).value
                email = sheet.cell(row=r, column=2).value
                month = sheet.cell(row=1, column=c).value
                clients.append(client)
                months.append(month)
                emails.append(email)
                unpaidMembers[client] = email
                #print('Line:', r, 'Column:', c, 'Client:', client, 'Email:', email, 'Month:', month)
                print('dictionary created successfully')

    cnv = canvas.Canvas(pastaApp+"\\test.pdf", pagesize=A4)
    cnv.drawString(10, 800, "Open Fee")
    cnv.drawString(130, 800, " - Client/Month/E-mail")
    cnv.drawString(10, 780, client)
    cnv.drawString(170, 780, month)
    cnv.drawString(350, 780, email)
    cnv.save()

root = Tk()
root.title("Create PDF")

btn_createPDF = Button(root, text="Check", command=createPDF)
btn_createPDF.pack(side="left", padx=10)

root.mainloop()

这是一个电子表格模型：https://prnt.sc/125jdcq