使用ReportLab在Python中打印PDF时偶发打印错误求助

使用ReportLab生成PDF并通过Python脚本打印时，出现无规律的偶发性错误：有时连续成功打印10次后触发，有时每隔一次就报错。出错时PDF会卡在打印队列中，只能通过插拔打印机暂时恢复，目前无法获取完整错误详情，希望排查代码或脚本层面的问题。

import os
import gspread
from oauth2client.service_account import ServiceAccountCredentials
import win32print
from reportlab.pdfgen import canvas
from reportlab.lib.pagesizes import landscape, portrait
from reportlab.lib.units import mm
from reportlab.pdfbase import pdfmetrics
from reportlab.pdfbase.ttfonts import TTFont

# Set up Google Sheets API credentials
scope = ['https://spreadsheets.google.com/feeds',
         'https://www.googleapis.com/auth/drive']
creds = ServiceAccountCredentials.from_json_keyfile_name('creds.json', scope)
client = gspread.authorize(creds)

# Set up printer name and font
printer_name = "Rollo Printer"
font_path = "arial.ttf"

# Register Arial font
pdfmetrics.registerFont(TTFont('Arial', font_path))

# Open the Google Sheet and select Label and Claims worksheets
sheet_url = "https://docs.google.com/spreadsheets/d/1eRO-30eIZamB5sjBp-Mz2QMKCfGxV037MQO8nS7G7AI/edit#gid=1988901382"
label_sheet = client.open_by_url(sheet_url).worksheet("Label")
claims_sheet = client.open_by_url(sheet_url).worksheet("Claims")

# Get the number of label copies to print
num_copies = int(label_sheet.acell("F2").value)

# Set up label filename and PDF canvas
label_file = "label.pdf"
label_canvas = canvas.Canvas(label_file, pagesize=landscape((400, 250)),bottomup=432)

# Write label text to PDF canvas
label_text = label_sheet.get_all_values()
x_pos = 10  # set initial x position
y_pos = 260  # set initial y position
line_height = 20  # set line height for text
label_canvas.setFont('Arial', 20)
for row in label_text:
    for col in row:
        textobject = label_canvas.beginText()
        textobject.setFont('Arial', 20)
        textobject.setTextOrigin(x_pos, y_pos)
        lines = col.split("\n")
        for line in lines:
            textobject.textLine(line)
            y_pos -= line_height
        label_canvas.drawText(textobject)
        x_pos += 145
        y_pos = 260
    x_pos = 10

# Save the label PDF and print to the printer
label_canvas.save()
for i in range(num_copies):
    os.startfile(label_file, 'printto', printer_name, "", 1)

# Set up claims filename and PDF canvas
claims_file = "claims.pdf"
claims_canvas = canvas.Canvas(claims_file, pagesize=landscape((400, 250)),bottomup=432)

# Write claims text to PDF canvas
claims_text = claims_sheet.get_all_values()
x_pos = 10
y_pos = 260  # set initial y position
line_height = 20
claims_canvas.setFont('Arial', 20)
for row in claims_text:
    for col in row:
        textobject = claims_canvas.beginText()
        textobject.setFont('Arial', 20)
        textobject.setTextOrigin(x_pos, y_pos)
        lines = col.split("\n")
        for line in lines:
            textobject.textLine(line)
            y_pos -= line_height
        claims_canvas.drawText(textobject)
        x_pos += 145
        y_pos = 260
    x_pos = 10

# Save the claims PDF and print to the printer
claims_canvas.save()
os.startfile(claims_file, 'printto', printer_name, "", 1)

排查建议 #

• 优化批量打印逻辑：当前循环调用os.startfile提交多份打印任务，易引发打印机队列拥堵或资源竞争。建议将多份标签合并为一个多页PDF后一次性打印，或在每次打印调用后添加2-3秒延迟，确保前一个任务处理完成。
• 确保PDF文件资源释放：canvas.save()后文件可能仍处于占用状态，直接打印易引发读取异常。可添加短暂延迟，或在打印完成后删除临时PDF文件（无需保留时），示例：

  import time
  label_canvas.save()
  time.sleep(1)  # 等待文件写入完成
  

• 替换打印方式为win32print：os.startfile依赖系统关联程序打开PDF，稳定性不足。改用win32api.ShellExecute直接发送打印任务，可更好控制流程并捕获错误：

  import win32api
  import time
  
  def print_pdf(pdf_path, printer_name):
      try:
          win32api.ShellExecute(
              0,
              "printto",
              pdf_path,
              f'"{printer_name}"',
              ".",
              0
          )
          time.sleep(2)
      except Exception as e:
          print(f"打印失败: {str(e)}")
  

• 修正PDF页面参数：当前设置bottomup=432属于非标准参数，可能导致打印机解析异常。建议移除该参数使用默认值，或用mm单位设置符合Rollo打印机的标准标签尺寸，比如landscape(100*mm, 63*mm)。
• 减少重复资源调用：代码中两次调用client.open_by_url打开同一份表格，可改为只打开一次，降低API资源消耗：

  spreadsheet = client.open_by_url(sheet_url)
  label_sheet = spreadsheet.worksheet("Label")
  claims_sheet = spreadsheet.worksheet("Claims")
  

• 添加错误捕获日志：在打印流程中加入try-except块，记录脚本执行时的异常信息，帮助定位偶发问题。

内容的提问来源于stack exchange，提问作者Anthony Madle