Platypus-在页面模板中使用多个框架

我正在为基于Django的网站编写一些PDF生成代码,使用ReportLab/Platypus生成PDF。

我已经对PageTemplate进行了子类化,这样我就可以进行一些一致的页面修剪,并包含了生成多列布局的代码,以满足需求。我目前已启用showBoundary=1进行调试。

然而,当我渲染两列布局时,我只看到第一个帧边界出现。可能出了什么问题?

class ReportPageTemplate(PageTemplate):
    def __init__(self, id='basic', columns=1, pagesize=A4, leftMargin=(2*cm), bottomMargin=(2.1*cm), colmargin=(0.5*cm)):
        (right, top) = pagesize
        right -= leftMargin
        top -= bottomMargin

        height = top - bottomMargin
        width = (right - leftMargin)
        # Subtract out blank space between columns
        colwidth = (width - ((columns - 1) * colmargin)) / columns

        frames = []
        for col in range(columns):
            left = leftMargin + (col * (colwidth + colmargin))
            frames.append(Frame(left, bottomMargin, colwidth, height, showBoundary=1))

        PageTemplate.__init__(self, id=id, frames=frames, pagesize=pagesize)

    def beforeDrawPage(self, canvas, doc):
        print self.id
        (width, height) = canvas._pagesize
        canvas.setLineWidth(0.2 * cm)
        canvas.line(0.5*cm, height - (2*cm), width - (0.5*cm), height - (2*cm))
        canvas.line(0.5*cm, (2*cm), width - (0.5*cm), (2*cm))