Dynamic Header in ReportLab

some_report.py

from functools import partial
# lots of other imports, esp for reportlab

# this function is ran for each page. 
def some_header(canvas,doc,content):

   canvas.saveState()

   P = Paragraph(content,style=some_style)
                  
   w, h = P.wrap(doc.width, doc.topMargin)
   
   P.drawOn(canvas, doc.leftMargin, doc.height+doc.topMargin-h)
   
   canvas.restoreState()
                    
# our dyanmic content
our_content = "Today is {}".format(datetime.now())                    

buf = io.BytesIO()
doc = SimpleDocTemplate(buf,   
                        pagesize=letter,
                        leftMargin=0.25*inch,
                        rightMargin=0.75*inch,
                        topMargin=1.5*inch, # make sure you have room for the header!
                        bottomMargin=0.25*inch,      
         )           

     
# here is where the currying happens. 
# I can set a function as a variable because Python is awesome like that.
header = partial(some_header, content=our_header)
      
# note that we have to specify it on the first and the rest of the pages.   
doc.build(self.doc_elements,
                canvasmaker=canvas_class,
                onFirstPage=header,
                onLaterPages=header
         )
buf.seek(0)