Python import error: Symbol not found, but the symbol <s>is</s> *is not* present in the file

I get this error when I try to import ssrc.spread:

ImportError: dlopen(/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/ssrc/_spread.so, 2): Symbol not found: __ZN17ssrcspread_v1_0_67Mailbox11ZeroTimeoutE

The file in question (_spread.so) includes the symbol:

$ nm _spread.so | grep _ZN17ssrcspread_v1_0_67Mailbox11ZeroTimeoutE
     U __ZN17ssrcspread_v1_0_67Mailbox11ZeroTimeoutE
     U __ZN17ssrcspread_v1_0_67Mailbox11ZeroTimeoutE

(twice because the file is a fat ppc/x86 binary)

EDIT:

okay, as James points out, the U means that the symbol is undefined but required by the object file.

With some more digging I've noticed (where I should have looked first...) these linker errors during compilation:

CC=g++ CXX=g++ g++-4.0 -arch ppc -arch i386 -isysroot /Developer/SDKs/MacOSX10.4u.sdk -fno-strict-aliasing -fno-common -dynamic -DNDEBUG -O3 -I../.. -I../.. -I/usr/local/include -I/Library/Frameworks/Python.framework/Versions/2.6/include/python2.6 -O2 -I/usr/local/include -std=c++98 -pipe -fno-gnu-keywords -fvisibility-inlines-hidden -o SsrcSpread.o -c SsrcSpread.cc
CC=g++ CXX=g++ /bin/sh ../../libtool --tag=CXX --mode=link g++-4.0 -arch ppc -arch i386 -isysroot /Developer/SDKs/MacOSX10.4u.sdk -bundle -undefined dynamic_lookup -F/Library/Frameworks -framework Python \
  -pthread -D_REENTRANT -pedantic -Wall -Wno-long-long -Winline -Woverloaded-virtual -Wold-style-cast -Wsign-promo -L../../ssrc -lssrcspread -L/usr/local/lib -ltspread-core  -o _spread.so SsrcSpread.o
mkdir .libs
g++-4.0 -arch ppc -arch i386 -isysroot /Developer/SDKs/MacOSX10.4u.sdk -bundle -undefined dynamic_lookup -F/Library/Frameworks -framework Python -pthread -D_开发者_运维技巧REENTRANT -pedantic -Wall -Wno-long-long -Winline -Woverloaded-virtual -Wold-style-cast -Wsign-promo -o _spread.so SsrcSpread.o -Wl,-bind_at_load  -L/Dev/libssrcspread-1.0.6/ssrc /Dev/libssrcspread-1.0.6/ssrc/.libs/libssrcspread.a -L/usr/local/lib -ltspread-core  
ld: warning: in ~/Dev/libssrcspread-1.0.6/ssrc/.libs/libssrcspread.a, file was built for unsupported file format which is not the architecture being linked (ppc)
ld: warning: in /Developer/SDKs/MacOSX10.4u.sdk/usr/local/lib/libtspread-core.dylib, file was built for unsupported file format which is not the architecture being linked (ppc)
ld: warning: in /Dev/libssrcspread-1.0.6/ssrc/.libs/libssrcspread.a, file was built for unsupported file format which is not the architecture being linked (i386)
ld: warning: in /Developer/SDKs/MacOSX10.4u.sdk/usr/local/lib/libtspread-core.dylib, file was built for unsupported file format which is not the architecture being linked (i386)

I'm also not entirely sure that the 10.4 sdk is the right one for compiling python modules (but switching to 10.6 didn't seem to help).

$ nm _spread.so | grep _ZN17ssrcspread_v1_0_67Mailbox11ZeroTimeoutE
     U __ZN17ssrcspread_v1_0_67Mailbox11ZeroTimeoutE
     U __ZN17ssrcspread_v1_0_67Mailbox11ZeroTimeoutE

The _spread.so file does not include the symbol, it is depending on it. The U means undefined.

I feel like there may be a version mismatch somewhere, perhaps between the headers and the library binaries. Do you have multiple versions installed?