Writes a single page pdf of width w mm and height h mm (defaults are A4) with a nrow x ncol grid traced out on it, to file outf. Grid is a thin line (thickness is lwd) coloured grey (default is very light grey) with dashing specified by dash length dl and space length sl.

pdfGrid.py

from fpdf import FPDF

def makeGrid(w=210.0, h=297.0, nrow=5, ncol=4, outf="grid.pdf", grey = 220, dl=3, sl=2, lwd=0.2):
    '''Writes a single page pdf of width w mm and height h mm (defaults are A4) with a nrow x ncol grid
traced out on it, to file outf.  Grid is a thin line (thickness is lwd) coloured grey (default is very
light grey) with dashing specified by dash length dl and space length sl.'''
    pdf = FPDF(orientation="P", unit="mm", format=(w,h))
    deltax = float(w)/ncol
    deltay = float(h)/nrow

    pdf.add_page()
    pdf.set_margins(0,0)
    pdf.set_line_width(lwd)
    pdf.set_draw_color(r=grey, g=grey, b=grey)

    for row in range(1,nrow):
        pdf.dashed_line(x1=0, y1=deltay*row, x2=w, y2=deltay*row, dash_length=dl, space_length=sl)
    for col in range(1,ncol):
        pdf.dashed_line(x1=deltax*col, y1=0, x2=deltax*col, y2=h, dash_length=dl, space_length=sl)
    pdf.output(outf)

if __name__ == "__main__":
    makeGrid(nrow=5, ncol=4, outf="grid020.pdf")
    makeGrid(nrow=7, ncol=3, outf="grid021.pdf")
    makeGrid(nrow=20, ncol=5, outf="grid100.pdf")