[dev] Gotchas

Do not use print before wx has taken over

A particularly nasty one - quoting @lojack:

@utumno: My initial though on where to look for Supierce's issue:

• Debug launcher starts in console mode, meaning stdout/stderr/stdin are initialized from the get go, so any print() statements will work at any point.
• Launching via the .pyw launcher, stdout/stderr are not initialized, and attempting to use a print() before they're initialized will cause an exception, followed by silent crash.
• Launching via the .pyw launcher, stdout/stderr are initialized once wxPython takes over - that is, sometime during the app.MainLoop() call in bash.py.
• WBSA has stdout/stderr initialized immediately, so it functions fine before wxPython takes over

So, based on the symptoms that launching in debug mode works fine, but non-debug does not, and yet no errors are printed, my guess would be that some message is attempting to be print()'ed, before wxPython takes over, so in non-debug mode it causes a crash. That's my initial though from what I've seen, I could be wrong though.

If you issue a print somevalue (as well as sys.stdout.flush etc etc) statement before wx has taken over the launcher will crash on its face - meaning no console outpout at all. You are in for a world of pain - see the @Supierce issue mentioned in the post above and in previous 20 posts.

See also the comments by Lojack at issue 67

Basically what crashes Bash to desktop on boot is C:\path\to\Mopy>c:\_\Python27\pythonw.exe "Wrye Bash Launcher.pyw" when there is a print + a flush before binding the stdout/stderr, as in:

@@ -273,11 +273,13 @@ def dump_environment():
 # Main ------------------------------------------------------------------------
 def main():
     bolt.deprintOn = opts.debug
     if len(extra) > 0:
         return
+    print 'CRASH'

+    sys.stdout.flush()
     # useful for understanding context of bug reports
     if opts.debug or hasattr(sys,'frozen'):
         # Standalone stdout is NUL no matter what.   Redirect it to stderr.
         # Also, setup stdout/stderr to the debug log if debug mode /
         # standalone before wxPython is up

C:\path\to\Mopy>c:\_\Python27\python.exe "Wrye Bash Launcher.pyw" works just fine