Ok, thank you. "10K+ users" is great and promising fact. After 5+ years of active python developing, I have decided to move to Tcl (you are right, "TCL" looks really wrong). I feel this language is fit to my tasks much better then python
Mind you, I don't know how many of those people write scripts. Plus, VMD also supports Python, though that was added years after Tcl.
Personally, I think Tcl is better for the types of scripting that the physical scientists (biologist, chemists, etc.) - most of my user base - want to do. However, as something they developed became more generally useful, I found I couldn't easily tweak it to be part of the larger system. OTOH, while Python is more complex than Tcl, I rarely feel the need to rewrite user code in Python into C++ code, so there's a more smooth transition between non-programmer code to experienced programmer code. That is one of the reasons I switched to Python.
On the flip side, IPython and others have developed script-like meta-languages which makes it easier to do some of the things that Tcl excels at.