NOTE: As of Sep. 4th, 2015, I can no longer reproduce this problem, using current versions of python and setuptools/distutils, in either python 2 or 3.
NOTE: I've answered this question myself and will be accepting the answer as soon as the system lets me, but this would appear to be the only instance of an English-language reference to the problem on the internet (according to google), so I thought I'd post both in hopes this can be useful.
I ran into a problem that I found impossible to debug when installing a python package of my own. It's a very simple package, with a flat structure (no subdirectories), and a few data files I need copied over at installation. With a few deletions for brevity, I have this:
spherical_functions
├── MANIFEST.in
├── __init__.py
├── spherical_functions.py
├── ladder_operator_coefficients.npy
└── setup.py
When installing from my source directory, I have no problems. But when I either switched to setuptools or installed with pip (which is needed for distribution), I get the error
can't copy 'ANIFEST.in': doesn't exist or not a regular file
Note the missing M at the beginning of that file name. I hacked into distutils a bit to verify that it was actually trying to copy ANIFEST.in, rather than just misreporting the name. Unfortunately, the trail ends there, because the rest of the setuptools code is hidden in some egg I don't understand.
A similar problem arises without a MANIFEST.in file, using just the package_data option to the setup function, where it misses the first letter of the data file, as in
error: can't copy 'adder_operator_coefficients.npy': doesn't exist or not a regular file
With a hint from this thread, I realized that I was making the mistake; I didn't really understand all the options to the setup function in setup.py. I had
package_dir={'spherical_functions': ''},
when I should have had
package_dir={'spherical_functions': '.'},
(Note the extra dot.) After including this, it seems to work just fine.
I might suggest that the resulting behavior is wrong in any case, suggesting a bug in setuptools and/or distutils. Or at least there could be a check to ensure that the user didn't do something stupid like I did...