Fix IndexError for getPage() of decryped file

[denis-osipov]

Issue #327
_flatten() method change flattenedPages to empty list when trying to get page and then test if file is encrypted and try to decrypt it. If it fails PdfReadError("file has not been decrypted") raise and flattenedPages not revert to None.
This fix allow to get page from PdfFileReader object after decryption.

[ameybh]

This works for me. I hope they merge it soon.

[MartinThoma]

I'm sorry that it took so long. I just became a maintainer of this project.

Do you @ameybhavsar24 / @denis-osipov have an example file / code snippet that shows the issue?

[MartinThoma]

I don't understand why this changes anything

[denis-osipov]

Hi, @MartinThoma

There is an encrypted pdf file to use in example:

import PyPDF2

pdfFileObj = open('example.pdf', 'rb')
pdfReader = PyPDF2.PdfFileReader(pdfFileObj)

try:
    # Can't get access to content of encrypted file. It's OK.
    print(pdfReader.getPage(0))
except PyPDF2.utils.PdfReadError as error:
    print('Expected error:', error)

# Password is correct:)
pdfReader.decrypt('test')

try:
    # Current behaviour is unexpected (for me): we decrypted file and now should
    # have access to its content. But we'll get an error here.
    print(pdfReader.getPage(0))
except IndexError as error:
    print('Unexpected error (file is decrypted now):', error)

Problem appears because _flatten() method sets self.flattenedPages before it tries to get pages and doesn't set it back to None in case of error. This PR just makes _flatten() to set self.flattenedPages to an empty array after it successfully got pages.

If there is a better solution or current behaviour is correct, just close the PR, please.

[codecov-commenter]

Codecov Report

Merging #359 (0417c1c) into main (733989a) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #359   +/-   ##
=======================================
  Coverage   69.57%   69.57%           
=======================================
  Files           9        9           
  Lines        3316     3316           
  Branches      783      783           
=======================================
  Hits         2307     2307           
  Misses        766      766           
  Partials      243      243           

Impacted Files	Coverage Δ
PyPDF2/pdf.py	72.36% <100.00%> (ø)

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[MartinThoma]

@denis-osipov Thank you for all the time and patience 🙏

This PR was just merged and will go into the next release (some time this month)

@ameybhavsar24 It's merged :-) It was by far not soon, but as the new maintainer I hope in future such things get resolved quicker.