When you start VMD, the VMD text console normally uses the Tcl
command interpreter to process what you type. In order to use the Python
interpreter, you have to tell VMD to switch to 'Python mode'. There are
three ways to do this: (1) Type gopython in the console window; (2)
pass -python as a command line option; or (3) put gopython on
the last line of your .vmdrc file. If VMD prints an error message
reporting that the Python interpreter is not available, your version
of VMD was not compiled with Python support; contact the VMD developers
for help. If all goes well, you should see Python command prompt '
' in the console window. To switch back to the Tcl interpreter, press
Ctrl-D as though you were exiting Python. Switching back and forth
between Python and Tcl does not destroy any of your work; all variables
and modules will still be defined until you exit VMD.
Typing 'gopython 
filename
', where
filename
is the name of a file
containing Python code will cause VMD to switch to Python mode, process the
file, then switch back to Tcl. In this way, you can embed Python functions
inside your Tcl scripts!
You can also type 'gopython -command "your code here" to run an arbitrary line of python code.