Most of the projects I work on require the use of several languages, and to me it's nice to be able to use the sharpest tool for each job. In a given day I might use one or more of C, C++, Python, sh (which possibly includes bits of sed/awk/etc), and make. In the not-far-distant past I switched between C, perl, python multiple times during the workday. The context switches aren't too jarring -- a stronger statement would be that I think it's easier to context-switch and use appropriate tools than it is to dance around a general purpose tool. E.g. substitution in perl or sed versus any other language.
Your point about sharper tools is absolutely fair and well-taken here. I wonder, though, are there diminishing returns when you have a language like Python that is a jack of so many trades? Is it worth the context switch for a tool that is only very slightly sharper?
It is usually worth the context switch, especially when (a) the project already has several tools in play and/or (b) the alternative is much sharper. A situation that calls for expect, or for sed, for example, is likely to be much more easily solved than with python.
On the other hand, if you're working on a system that is almost exclusively python, it wouldn't make sense to use something only "very slightly sharper". E.g. calling out to perl to do some one-liner that needs 5 lines in python.
