用 Python 寫給電腦用的開立發票程式：在視窗中輸入客戶、項目、稅額與合計，產生可列印的發票

The windows

1. Invoices: the list of past invoices with number, client, date and total; buttons New, Open and Save as PDF.
2. New invoice: client from a drop-down list, lines with description, hours and rate, tax rate, and the total updated as you type.
3. Clients: name, address and email, added once and picked from the list afterwards.

A part of the code

def update_total(self, *_):
    """Adds up the lines and the tax and shows the total under the table."""
    subtotal = sum(line.hours * line.rate for line in self.lines)
    tax = round(subtotal * self.tax_rate.get() / 100, 2)
    self.subtotal_label.config(text=f"Subtotal: {subtotal:,.2f}")
    self.tax_label.config(text=f"Tax: {tax:,.2f}")
    self.total_label.config(text=f"Total: {subtotal + tax:,.2f}")

In the archive

• invoice_maker.py, the program, about 700 lines;
• invoices.db, made on the first run, which keeps the clients and invoices;
• settings.example.ini for your name, address and invoice number format;
• requirements.txt with the one extra library, reportlab, which writes the PDF;
• README: how to install Python, start the program and build an .exe with PyInstaller.

The program runs on the client's own computer. We do not build installers, sign the program or publish it.