Fix XML Page template files in Python 3

[ale-rt]

Fixes #319

[ale-rt]

Without the patch the ptest fail like:

Error in test testXMLPageTemplateFile (Products.PageTemplates.tests.testZopePageTemplate.ZopePageTemplateFileTests)
Traceback (most recent call last):
  File "/usr/lib/python3.6/unittest/case.py", line 59, in testPartExecutor
    yield
  File "/usr/lib/python3.6/unittest/case.py", line 605, in run
    testMethod()
  File "/home/ale/Code/python/Zope/src/Products/PageTemplates/tests/testZopePageTemplate.py", line 234, in testXMLPageTemplateFile
    PageTemplateFile(filename).pt_render(),
  File "/home/ale/Code/python/Zope/src/Products/PageTemplates/PageTemplate.py", line 83, in pt_render
    showtal=showtal)
  File "/home/ale/.buildout/eggs/zope.pagetemplate-4.3.0-py3.6.egg/zope/pagetemplate/pagetemplate.py", line 128, in pt_render
    raise PTRuntimeError(str(self._v_errors))
   - Warning: Compilation failed
   - Warning: builtins.TypeError: cannot use a string pattern on a bytes-like object
zope.pagetemplate.pagetemplate.PTRuntimeError: ['Compilation failed', 'builtins.TypeError: cannot use a string pattern on a bytes-like object']

The compilation fails when reaching this line:

Zope/src/Products/PageTemplates/engine.py

Line 99 in 6dcd4c7

text, count = re_match_pi.subn(sanitize, text)

[icemac]

Does this PR aim to fix #319?

[ale-rt]

Yes @icemac!
This fixed https://jenkins.plone.org/view/PLIPs/job/plip-py3/790/testReport/junit/Products.CMFPlacefulWorkflow/tests/exportimport_txt/
Which is now passing https://jenkins.plone.org/view/PLIPs/job/plip-py3/795/testReport/junit/Products.CMFPlacefulWorkflow/tests/exportimport_txt/

[davisagli]

This mostly looks great but I have one concern.

[davisagli]

Maybe it would be better to let the exception happen rather than swallowing it and returning bytes which will probably just fail later?

[icemac]

+1

[ale-rt]

If I remove the try/except the tests from test_sniffer_xml_utf16_be and test_sniffer_xml_utf16_le will fail because the regexp in encodingFromXMLPreamble method will fail to match the encoding.

[icemac]

I share the concern of @davisagli

[icemac]

+1

[ale-rt]

I removed the try/except but I had to add an encoding parameter to the PageTemplateFile constructor (as we have on the Python3 open function).
The reason is that otherwise there is no proper reliable way to detect the encoding a part from checking the first bytes of the file (which might also be an option).