Reportlab : How to switch between portrait and landscape?

I am using reportlab to generate a pdf report automatically from dynamic data. As the content sometimes is too large to be displayed in portrait, I am trying to switch to landscape for large content.

Here is how my report generation works :

Main function :

doc = DocTemplate(...)           //Doctemplate is a customed BaseDocTemplate class
array = []
some_data= "Here is some data displayed in portrait" 

array.append(Paragraph(some_data))

large_data = "this data is too large to be displayed in portrait"
array.append(Paragraph(large_data))

... // Some more data is added after this

doc.build(array, canvasmaker=NumberedCanvas)

What I am looking for is a way to be able to switch from portrait to landscape at each step, as I don't know the number of pages that will be needed to display it. I am still new to reportlab and even a bit with python, so I do not see how I can use the solutions provided by reportlab (PageTemplates, flowables) properly as I am building the whole document at the end.

Here are my other useful classes for this case :

class DocTemplate(BaseDocTemplate, ):
def __init__(self, filename, **kw):
    apply(BaseDocTemplate.__init__, (self, filename), kw)
    f = Frame(2.6*cm, 2.8*cm, 16*cm, 22.7*cm, id='f')
    pt = PageTemplate('RectPage', [f], onPage=beforeDrawPage, onPageEnd=afterDrawPage)
    //beforeDrawPage and afterDrawPage fill the headers of the page (that also need to be in landscape)
    self.addPageTemplates(pt)

I think I shall add another page template or frame, but I don't see how i can switch from one to the other during the data appending phase.

class NumberedCanvas(canvas.Canvas):
def __init__(self, *args, **kwargs):
    canvas.Canvas.__init__(self, *args, **kwargs)

    self._saved_page_states = []

def showPage(self):
    self._saved_page_states.append(dict(self.__dict__))
    self._startPage()

def save(self):
    """add page info to each page (page x of y)"""
    num_pages = len(self._saved_page_states)
    for state in self._saved_page_states:
        self.__dict__.update(state)
        self.draw_page_number(num_pages)
        canvas.Canvas.showPage(self)
    self.setTitle("Title")
    canvas.Canvas.save(self)
    self._doc.SaveToFile(self._filename, self)

def draw_page_number(self, page_count):
    self.setFont("Helvetica", 11)
    self.drawRightString(18.5*cm, 26.8*cm,
        "PAGE %d / %d" % (self._pageNumber, page_count))

I hope I did'nt forgot anything to be clear.

Many thanks in advance.