Update dumpstyle.py

[tbpassin]

Added from future import absolute_import, and adjusted import statement for Py2-3 compatibility.

Corrected directory location in main routine to be relative to rst2pdf package (os.path.listdir('styles') wouldn't work if we weren't running from the right directory).

[tbpassin]

Cannot be tested on Windows with autotest, because that only runs on Linux. To test:

py38 -m rst2pdf.dumpstyle # or py27 instead

This must run with no errors. Previous errors I got before I fixed the listdir() were

Traceback (most recent call last):
  File "C:\Users\tom\AppData\Local\Programs\Python\Python38\lib\runpy.py", line 192, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "C:\Users\tom\AppData\Local\Programs\Python\Python38\lib\runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "d:\Tom\git\rst2pdf\rst2pdf\dumpstyle.py", line 161, in <module>
    for fname in [os.path.join('styles', x) for x in os.listdir('styles') if x.endswith('.json')]:
FileNotFoundError: [WinError 3] The system cannot find the path specified: 'styles'

[tbpassin]

Sorry to have to amend this pull request. This is my first time pushing from a cloned repo, and I'm still getting used to Guthub Desktop.

[akrabat]

Can you explain how to test this? i.e. what should I type to see a failure before this change is applied and then after applying, I will see it working?

[tbpassin]

Rob, for my test procedure please see my comment at #826. For the dumpstyle module in the Master branch, I got these tracebacks:

C:\Users\tom>py38 -m rst2pdf.dumpstyle
Traceback (most recent call last):
  File "C:\Users\tom\AppData\Local\Programs\Python\Python38\lib\runpy.py", line 192, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "C:\Users\tom\AppData\Local\Programs\Python\Python38\lib\runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "D:\Tom\git\rst2pdf\rst2pdf\dumpstyle.py", line 12, in <module>
    from rson import loads as rloads
ModuleNotFoundError: No module named 'rson'

and for Python 2.7:

C:\Users\tom>python -m rst2pdf.dumpstyle
Traceback (most recent call last):
  File "c:\python27\lib\runpy.py", line 174, in _run_module_as_main
    "__main__", fname, loader, pkg_name)
  File "c:\python27\lib\runpy.py", line 72, in _run_code
    exec code in run_globals
  File "D:\Tom\git\rst2pdf\rst2pdf\dumpstyle.py", line 160, in <module>
    for fname in [os.path.join('styles', x) for x in os.listdir('styles') if x.endswith('.json')]:
WindowsError: [Error 3] The system cannot find the path specified: 'styles\\*.*'

So for Python3.8, the import of rson failed, and for Python 2.7, the module couldn't find the styles directory. I had to fix both problems to make the module run for both Python versions. I hate to ask for two unrelated changes in one pull request (the import statement, and locating the styles directory), but they are both needed to run successfully.