cannot open display: :0.0

For the Nth time, I have had to remember how to configure the X11 display variable to cope with this error
Gtk-WARNING **: cannot open display: :0.0
when running vpython on Mac OS X

First, I need to be running x11 (I knew that)
Second, I need to run the appropriate version of python /sw/bin/python2.4 (I knew that)

Third, my .tcshrc file needed to contain this line
setenv DISPLAY :1.0
Now that's unusual. Usually, it's 0.0

indeed, a few days later and I have to set it back to 0.0
why??


You've got to get them all right all the time (I know that, and I resent it.)