Add custom metadata to matplotlib pdfs

mpl_pdf_metadata.py

"""
Write metadata to pdf files with no warnings.
Useful for provenance, and in this way we can suppress warnings for end users of a larger application
"""

from matplotlib.backends.backend_pdf import PdfPages
import matplotlib.pyplot as plt
import numpy as np
import warnings

##############################################################################

## Generate some data that we want to plot
x_data = np.linspace(0.0, 4.0, 101)
y_data = np.sin(x_data)

##############################################################################

## Save with metadata in savefig call
## This generates warnings! But still works
fig, axes = plt.subplots(1,1)
axes.plot(x_data, y_data, marker='o', linestyle='', color='C0')
fig.savefig("mpl_mdata_savefig.pdf", metadata={"Author": "Sam", "foo": "bar", "baz": "3"})

##############################################################################

## Let's write a function that let's us do this without the warnings!
def save_custom_pdf_metadata(fig_obj, target_path, metadata):
	## Enter the context manager for the pdf object
	with PdfPages(target_path) as pdf_obj:
		## Get metadata InfoDict object
		infodict = pdf_obj.infodict()
		## Suppress warnings, but ONLY for the metadata addition step
		with warnings.catch_warnings():
			## Iterate over metadata elements and add them to infodict
			for key, value in metadata.items():
				infodict[key] = value
		## Save the current figure
		pdf_obj.savefig(fig_obj)
		## Watch out for:
		## - more possible kwargs in the call to savefig
		## and/or
		## - needs to be filtered by format at a higher level, as this only works for pdf!
	## 
	return fig_obj

## Now using the custom function
fig, axes = plt.subplots(1,1)
axes.plot(x_data, y_data, marker='o', linestyle='', color='C0')
save_custom_pdf_metadata(fig, "mpl_mdata_suppressed.pdf", metadata={"Author": "Sam", "foo": "bar", "quux": "3"})

## In a real application, the metadata will be generated automatically
## All the user needs to do is say "here's the fig object, save this (as a pdf)".