Split up and/or remove duplicate certificates from a PEM-formatted CA bundle (e.g. ca-bundle.crt)

split_ca_cert.py

#!/usr/bin/env python

"""
Split up and remove duplicate CA certificates from a bundle (e.g.
ca-bundle.crt).

.. note::

    This script will preserve comments and certificate metadata at
    the expense of possibly missing duplicates (that don't have the
    same leading comments/metadata).  It does *not* preserve ordering.
"""

ca_bundle_path = "/etc/ssl/certs/ca-bundle.crt"
new_ca_bundle_path = "/etc/ssl/certs/ca-bundle.crt.new"
cert = ""
ca_certs = set() # Using a set to prevent (exact) duplicates
for line in open(ca_bundle_path, 'rb'):
    cert += line
    if '-----END CERTIFICATE-----' in line:
        ca_certs.add(cert)
        cert = ""

# Now we've got all our certificates in the ca_certs variable
# with duplicates removed.  Write them out to the new file:
with open(new_ca_bundle_path, 'wb') as ca_bundle:
    ca_bundle.write(''.join(ca_certs))

Very useful and handy Script.
Thank you @liftoff 👍 💯

Quick note: I had to open the file in 'r' mode instead of 'rb' to do the concatenations of lines(str type) using python v3+