Why does $Path change when I examine it in new cell after I just changed it? This is really driving me crazy. In one cell, I change $Path by removing from it un-needed paths that I do not want for the duration of a computation I will be doing.

Immediatly after, in new cell, I type $Path and see it was changed ok. Now, I open a new cell, and do the same. I type$Path again, and now I see some of the Paths I removed are back again! Here is a screen shot from my notebook now

You can see the variable $Path now has changed, on its own. This is what I type $Path =DeleteCases[$Path, "C:\\Users\\me"];$Path =DeleteCases[$Path, "."];$Path =DeleteCases[$Path,"C:\\Program Files\\Wolfram Research\\Mathematica\\8.0.4\\AddOns\\LegacyPackages"];$Path =DeleteCases[$Path,"C:\\Users\\me\\AppData\\Roaming\\Mathematica\\Autoload"];$Path =DeleteCases[$Path,"C:\\Users\\me\\AppData\\Roaming\\Mathematica\\Kernel"];$Path =DeleteCases[$Path,"C:\\Users\\me\\AppData\\Roaming\\Mathematica\\Applications"];$Path =DeleteCases[$Path,"C:\\ProgramData\\Mathematica\\Applications"];$Path =DeleteCases[$Path,"C:\\ProgramData\\Mathematica\\Autoload"];$Path =DeleteCases[$Path,"C:\\ProgramData\\Mathematica\\Kernel"];$Path=DeleteCases[$Path,"C:\\Program Files\\Wolfram Research\\Mathematica\\8.0.4\\Documentation\\English\\System"];  Then in new cell $Path


Then in new cell the same. And now the $Path has been reset. I noticed this when I was calling Leonid function he posted, and in it, it uses $Path, but I noticed I was getting packages that should not show up since I changed the $Path before calling it. This is really strange. I am using V 8.0.4 on windows 7 edit Just installed version 9. Not able to reproduce this. Using the same PC, same notebook, same steps. So it looks like, whatever it was, is fixed in Version 9. - Regardless of the origin of this, you can use Block[{$Path= DeleteCases[\$Path,...]},...] around the function, to get rid of those directories dynamically. –  Leonid Shifrin Nov 28 '12 at 18:41
Thanks, Nasser,but my comment does not really explain what you observed, so it won't make a good answer to your question. –  Leonid Shifrin Nov 29 '12 at 8:10