PyFPDF can't add page while specifying the size
Your problem is that two packages of pypdf exist, fpdf and fpdf2. They both use from fpdf import FPDF, but only fpdf2 has also a format= keyword in the add_page() method.
So you need to install the fpdf2 package.
on pyfpdf documentation it is said that it is possible to specify a format while adding a page (fpdf.add_page(orientation = '', format = '', same = False)) but it gives me an error when specifying a format.
error:

pdf.add_page(format = (1000,100)) TypeError: add_page() got an
  unexpected keyword argument 'format'

i've installed pyfpdf via pip install and setup.py install but it doesnt work in both ways
how can i solve this?