5. Packing and unpacking

In many cases you may want to plot data that is stored in a separate external file. In order for this to work, the external data file must be included, which can be achieved by packing and unpacking the data into the PyPDF file.

5.1. Packing files

In this section we show how to write a script that opens data from an external Excel file and reads the title and axis label from an extrnal text file, where both files are embedded in the PyPDF file.

Create an excel file data.xlsx and fill the Excel file with data, e.g. the first 10 numbers of the Fibonacci sequence:

_images/excel_data.png

Next, create a text file title.txt and add names for the plot title and axes:

_images/notepad_title.png

Finally, create a new python file packing.py that looks as follows:

import pypdfplot.backend.unpack
import matplotlib.pyplot as plt
import pandas as pd

df = pd.read_excel('data.xlsx')
plt.plot(df.x,df.y,'o')

with open('title.txt','r') as f:
    title = f.readline()
    xlabel = f.readline()
    ylabel = f.readline()

plt.title(title)
plt.xlabel(xlabel)
plt.ylabel(ylabel)

plt.savefig('packing.pdf',
            pack_list = ['data.xlsx',
                         'title.txt'],
            cleanup = True,
            )

By appending the filenames data.xlsx and title.txt to the pack_list list, the files will be embedded in the output PyPDF file.

Note that in order for this script to work, the next time it is ran these files must be extracted before Python attempts to open them. To make sure they are extracted before they are referenced, the PyPDF file can be unpacked immediately when the pypdfplot backend is loaded, by importing pypdfplot.backend.unpack instead of importing just pypdfplot.backend.

Finally, the keyword cleanup = True was passed to savefig() to toggle whether the external files will be removed (cleanup = True, default) or not (cleanup = False).

Warning:By passing cleanup = True (which is the default!), the local files are removed. If the original Python script without the files embedded is now ran again, an exception will be raised because the local files no longer exist. Therefore when cleanup = True is passed, the only way the script can be ran again is by opening the output PyPDF file, which has the external files embedded.

After running the script, the packing.py file is replaced by the output PyPDF file packing.pdf:

_images/packing_plot.png

As can be seen in the “Attachments” list, the external files data.xlsx and title.txt have been embedded in the PyPDF file, in addition to the generating Python script.

5.2. Unpacking files

A PyPDF file that has files embedded must always be unpacked at the beginning of the script (see Packing files), so unpacking files is just a matter of not removing the files after they have been extracted.

This is done by simply passing the keyword argument cleanup = False.