To launch pycrossword, run pycross on Linux/Mac or pycross.bat on Windows to launch the pycrossword UI app. This should work regardless of whether you are running Python in a virtual environment or without one.
To launch the app manually, run:
python cwordg.py [optional command-line params]
from your pycross directory.
The command-line parameters that can be passed to cwordg.py are as follows:
--rows: number of rows in the new crossword (default = 15)
--pattern: pattern number for the new crossword (one of 1...6, default = 1)
-e or --empty: don't open or create a crossword
-a or --addsrc + "{source data}": add a word source (see pycross/forms.py/WordSrcDialog for description of the source data structure)
Read the following sections of this manual to learn what these parameters mean.
Alternatively, you can register the pycrossword file associations at initial run (go to Settings > Common > Register file associations). After that, you can launch the app by double-clicking crossword files (like *.xpf or *.ipuz) or settings files (*.pxjson).