Why forcing little endian?

[ziyuang]

At https://github.com/rogersce/cnpy/blob/master/cnpy.cpp#L94, I can see

loc1 = header.find("descr")+9;
bool littleEndian = (header[loc1] == '<' || header[loc1] == '|' ? true : false);
assert(littleEndian);

Why is there a constraint?