Writing multiple matplotlib figures to PDF file

Question

I have a list of Matplotlib figures that are saved as bytes in pdf format and base64 encoded. I wish to save these figures to a PDF file with the following code:

with open('result.pdf', 'wb') as f:
    for fig in f_list:
        f.write(base64.b64decode(fig))

The file is created successfully but it seems like only the last figure is saved to the file. What am I doing wrong??

Can you append PDFs to each other like that? Do you have something like poppler installed? You could use pdfunite if you did. — Mad Physicist
– Mad Physicist, Commented Jan 12, 2022 at 3:43
wb overwrites the file. You can append with ab, but that doesn't fix your problem. That appends bytes. If you want to add pages to a PDF, then you'll need a Python library that knows how to do that. — Silvio Mayolo
– Silvio Mayolo, Commented Jan 12, 2022 at 3:52
If you have more than one fig in the list, they will all be written. How do you know there is only one? Are you using a pdf reader? You could sum the size of the decoded figures in the loop and see if that matches file size. — tdelaney
– tdelaney, Commented Jan 12, 2022 at 4:02
Turns out all the figures were being written to the file but only the last page was being displayed. I used PyPDF2 to fix this — Mosky1970
– Mosky1970, Commented Jan 13, 2022 at 8:40

Mosky1970 · Accepted Answer · 2022-01-13 08:44:52Z

1

All the figures are being written to the file but only the last page was being displayed. I had to use a PyPDF2 to save and display all the pages.

The implementation is below:

from PyPDF2 import PdfFileReader, PdfFileWriter


writer = PdfFileWriter()
for fig in f_list:
    decoded_data = base64.b64decode(fig)
    reader = PdfFileReader(io.BytesIO(decoded_data)) # convert the figure to a stream object
    writer.addPage(reader.getPage(0))

with open('result.pdf', 'wb') as pdf_file:
    writer.write(pdf_file)

answered Jan 13, 2022 at 8:44

Mosky1970

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