I don't think that this is a python issue, because of this:

[root@localhost ~]# curl -O http://wm.exchanger.ru/asp/XMLWMList.asp?exchtype=1
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
[root@localhost ~]# curl -O http://wm.exchanger.ru/asp/XMLWMList.asp?exchtype=1
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  9299  100  9299    0     0  15471      0 --:--:-- --:--:-- --:--:-- 22134


I done two request in rapid succession and into first i got a redirect to

	0x0000:  4500 008f 3abb 0000 3206 1d98 d49e ad94  E...:...2.......
	0x0010:  ac10 01d3 0050 b220 47ee 6cdb 8b3d 6233  .....P..G.l..=b3
	0x0020:  5011 0001 edc2 0000 4854 5450 2f31 2e31  P.......HTTP/1.1
	0x0030:  2033 3032 204d 6f76 6564 2054 656d 706f  .302.Moved.Tempo
	0x0040:  7261 7269 6c79 0d0a 436f 6e74 656e 742d  rarily..Content-
	0x0050:  4c65 6e67 7468 3a20 300d 0a4c 6f63 6174  Length:.0..Locat
	0x0060:  696f 6e3a 202f 6173 702f 584d 4c57 4d4c  ion:./asp/XMLWML
	0x0070:  6973 742e 6173 703f 6578 6368 7479 7065  ist.asp?exchtype
	0x0080:  3d31 3f34 6430 3266 3136 380d 0a0d 0a    =1?4d02f168....

as you can see, the ?4d02f168 part comes from the site, hence the 500 error from second request.

In the second try, i got correct response.

The weird thing is that into other systems, no curl request triggers a redirect from the site,
and in centOS only we have this weird behaviour.