Python : win32print - data does not leave the print queue

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28-08-2024

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You're encountering a common issue when using win32print to send print jobs. While the code appears correct, it often fails to print directly to the printer, instead leaving the data stuck in the queue.

Here's a breakdown of the problem and how to fix it:

Understanding the Problem:

• Print Spooler and Drivers: Windows uses a print spooler to manage print jobs. When you send a print job, it's placed in a queue and processed by the printer driver. The driver interprets the data and sends it to the printer.
• RAW Data: The win32print library allows you to send "raw" data to the printer. This assumes the printer driver can directly understand the raw data format.
• Compatibility and Limitations: Many printers, particularly network printers, require specific data formats or protocols. Sending raw data might not be compatible with the printer's driver and configuration.

Troubleshooting and Solutions:

1. Verify Printer Driver and Configuration:

   • Compatibility: Ensure that the printer driver installed on your system is compatible with the printer model.
   • Port Settings: Check the printer's port settings in the Windows Print Management console. It should be configured correctly for the network connection.
   • Driver Settings: Explore the printer's driver settings for options like "raw data printing" or "direct printing".

2. Use a Different Print Library:

   • pywin32: Explore the pywin32 library, which provides more comprehensive access to Windows functions and might offer alternative printing methods.
   • Third-Party Libraries: Consider libraries specifically designed for printing, such as reportlab or pypdf2. These libraries can handle document generation and formatting.

3. Alternative Printing Methods:

   • Intermediate File: Generate a temporary file (e.g., a PDF or text file) containing your data, then use standard printing functionality in Python to send the file to the printer.
   • System Commands: Use the os.system function to execute Windows print commands (cmd /c print <file path>).

4. Debugging and Testing:

   • Check Print Queue: Monitor the printer queue in Windows to see if the job is being added or processed.
   • Error Handling: Implement try-except blocks to catch any exceptions raised by the win32print functions.
   • Logging: Log the print job's status, data sent, and any error messages to help identify issues.

Code Example with Intermediate File:

import win32print
import os

# Printer name
printer_name = "Brother DCP-L5652DN Printer"

# Create temporary file
file_path = "temp_print.txt"
with open(file_path, "w", encoding="utf-8") as f:
    f.write("This is a test printing from Python!")

# Print using system command
os.system(f'cmd /c print "{file_path}" /d "{printer_name}"')

# Delete temporary file
os.remove(file_path)

print("Print job sent!")

Remember:

• Testing: Always test your code on a printer you have direct access to for troubleshooting.
• Security: Be cautious about using external libraries or executing system commands.
• Customization: The specific method will depend on your printer model, driver, and network configuration.

By understanding the print spooler and printer driver's behavior, using alternative libraries or methods, and carefully debugging your code, you can overcome this common "print queue" issue and successfully send print jobs from your Python program.