Robustness and strict=False

PDF is specified in various versions. The specification of PDF 2.0 has 1003 pages. This length makes it hard to get everything right. As a consequence, a lot of PDF files are not strictly following the specification.

If a PDF file does not follow the specification, it is not always possible to be certain what the intended effect would be. Think of the following broken Python code as an example:

# Broken
function (foo, bar):

# Potentially intended:
def function(foo, bar):

# Also possible:
function = (foo, bar)

Writing a parser you can go two paths: Either you try to be forgiving and try to figure out what the user intended, or you are strict and just tell the user that they should fix their stuff.

pypdf gives you the option to be strict or not.

pypdf has two core objects:

Only the PdfReader has a strict parameter, since presumably you do not want to write a non-conforming PDF.

Choosing strict=True means that pypdf will raise an exception if a PDF does not follow the specification.

Choosing strict=False means that pypdf will try to be forgiving and do something reasonable, but it will log a warning message. It is a best-effort approach.