Question

I am trying to produce a PDF document with different odd/even page layouts (to allow asymmetric borders for binding) using Python 2.7 and ReportLab. To further complicate matters I am trying to produce two-columns per page.

def WritePDF(files):

    story = []
    doc = BaseDocTemplate("Polar.pdf", pagesize=A4, title = "Polar Document 5th Edition")

    oddf1  = Frame(doc.leftMargin, doc.bottomMargin, doc.width/2-6, doc.height, id='oddcol1') 
    oddf2  = Frame(doc.leftMargin+doc.width/2+6, doc.bottomMargin, doc.width/2-6, doc.height, id='oddcol2')
    evenf1 = Frame(doc.leftMargin, doc.bottomMargin, doc.width/2-6, doc.height, id='evencol1') 
    evenf2 = Frame(doc.leftMargin+doc.width/2+6, doc.bottomMargin, doc.width/2-6, doc.height, id='evencol2')
    doc.addPageTemplates([PageTemplate(id='EvenTwoC',frames=[evenf1,evenf2],onPage=evenFooter),
                          PageTemplate(id='OddTwoC', frames=[oddf1, oddf2], onPage=oddFooter)])


    ...

    story.append(Paragraph(whatever, style))

What I can’t figure out is how to make ReportLab alternate between right and left (or odd and even) pages. Any suggestions?

Answer 1

I found the solution I guess ! 🙂

I had to dig into the source code. I found the solution in the file reportlab/platypus/doctemplate.py on line 636. It’s not the first time I had to do this, as the documentation is pretty limited…

Now, what I found:

def handle_nextPageTemplate(self,pt):
        '''On endPage change to the page template with name or index pt'''
        if type(pt) is StringType:
            # ... in short, set self._nextPageTemplate
        elif type(pt) is IntType:
            # ... in short, set self._nextPageTemplate
        elif type(pt) in (ListType, TupleType):
            #used for alternating left/right pages
            #collect the refs to the template objects, complain if any are bad
            c = PTCycle()
            for ptn in pt:
                found = 0
                if ptn=='*':    #special case name used to short circuit the iteration
                    c._restart = len(c)
                    continue
                for t in self.pageTemplates:
                    if t.id == ptn:
                        c.append(t)
                        found = 1
                if not found:
                    raise ValueError("Cannot find page template called %s" % ptn)
            if not c:
                raise ValueError("No valid page templates in cycle")
            elif c._restart>len(c):
                raise ValueError("Invalid cycle restart position")

            #ensure we start on the first one
            self._nextPageTemplateCycle = c.cyclicIterator()
        else:
            raise TypeError("argument pt should be string or integer or list")

And I checked where this self._nextPageTemplateCycle is used, so this is what I think should work (not tested though):

story = []
# ...
# doc.addPageTemplates([...])

story.append(NextPageTemplate(['pageLeft', 'pageRight'])) # this will cycle through left/right/left/right/...

story.append(NextPageTemplate(['firstPage', 'secondPage', '*', 'pageLeft', 'pageRight'])) # this will cycle through first/second/left/right/left/right/...

Add this to story once, when you want to start alternating pages. Use another normal NextPageTemplate to stop this cycle (because in the source, there’s a del self._nextPageTemplateCycle if you do that).

Hope it helps, and do say if it works, I can’t make sure right now, but I will!