append page to existing pdf file using python (and matplotlib?)

Question

I would like to append pages to an existing pdf file.

Currently, I am using matplotlib pdfpages. however, once the file is closed, saving another figure into it overwrites the existing file rather than appending.

from matplotlib.backends.backend_pdf import PdfPages
import matplotlib.pyplot as plt



class plotClass(object):
    def __init__(self):
        self.PdfFile='c:/test.pdf'
        self.foo1()
        self.foo2()


    def foo1(self):
        plt.bar(1,1)
        pdf = PdfPages(self.PdfFile)
        pdf.savefig()
        pdf.close()

    def foo2(self):
        plt.bar(1,2)
        pdf = PdfPages(self.PdfFile)
        pdf.savefig()
        pdf.close()

test=plotClass()

I know appending is possible via multiple calls to pdf.savefig() before calling pdf.close() but I would like to append to pdf that has already been closed.

Alternatives to matplotlib would be appreciated also.

Answer 1

You may want to use pyPdf for this.

# Merge two PDFs
from PyPDF2 import PdfFileReader, PdfFileWriter

output = PdfFileWriter()
pdfOne = PdfFileReader(open("path/to/pdf1.pdf", "rb"))
pdfTwo = PdfFileReader(open("path/to/pdf2.pdf", "rb"))

output.addPage(pdfOne.getPage(0))
output.addPage(pdfTwo.getPage(0))

outputStream = open(r"output.pdf", "wb")
output.write(outputStream)
outputStream.close()

example taken from here

Thereby you detach the plotting from the pdf-merging.

Answer 2

I searched around for a while but could not find a way to append to the same pdf file after re-opening it elsewhere in the program. I ended up using dictionaries, that way I can store the figures to the dictionary for each pdf I'm interested in creating and write them to pdfs at the end. Here is an example:

dd = defaultdict(list)  #create a default dictionary
plot1 = df1.plot(kind='barh',stacked='True') #create a plot
dd[var].append(plot1.figure) #add figure to dictionary

#elsewhere in the program
plot2 = df2.plot(kind='barh',stacked='True') #another plot
dd[var].append(plot2.figure) #add figure to dictionary

#at the end print the figures to various reports
for var in dd.keys():
    pdf = PdfPages(var+.'pdf') #for each dictionary create a new pdf doc
    for figure in dd[k]:
        pdf.savefig(figure)   #write the figures for that dictionary
    pdf.close()