Question about git svn handling svn external

I use a python script which calls git svn clone based on a text file
built from the svn externals of the form

dir1 url1
dir2 url2

to create a git project. Each subdirectory of course will have its own
.git and point back to the original svn repository so that I can
change a particular subdirectory.

For example, I have dirn from urln/trunk built and I want to change it
to urln/branches/mybranch.

Is there a good way of doing this without deleting everything under it?

If I wipe out the dirn directory, I would wipe out the externals that
came in with urln and I would have to pick up all the entries that
follow. I do not want to pick up the external pointer from svn as I
might not actually be using all of those. I want to only bring in the
entries from the configuration file.  Of course, it would be more
useful if someone has already done it.

The project that I am on would like to use python for this, but if
someone has already written something, the language would not matter.



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