fix for python 2.6 compatibility
fix for python 2.6 compatibility

pmaunz/pyqtgraph,duguxy/pyqtgraph,hiuwo/acq4,vallsv/pyqtgraph,onlyjus/pyqtgraph,Lx37/pyqtgraph,ericdill/pyqtgraph,acq4/acq4,pbmanis/acq4,hiuwo/acq4,welshjf/pyqtgraph,meganbkratz/acq4,tropp/acq4,wonkoderverstaendige/MausverPyler,pbmanis/acq4,tropp/acq4,duguxy/pyqtgraph,Lx37/pyqtgraph,mgraupe/acq4,derricw/pyqtgraph,pmaunz/pyqtgraph,gvalentine/pyqtgraph,mgraupe/acq4,tropp/acq4,carlomt/dicom_tools,hiuwo/acq4,hiuwo/acq4,derricw/pyqtgraph,mgraupe/acq4,campagnola/acq4,acq4/acq4,mpvismer/pyqtgraph,jlombacher/pyqtgraph,carlomt/dicom_tools,welshjf/pyqtgraph,petebachant/pyqtgraph,acq4/acq4,stscieisenhamer/pyqtgraph,ddamiani/pyqtgraph,gvalentine/pyqtgraph,ddamiani/pyqtgraph,ng110/pyqtgraph,campagnola/acq4,mpvismer/pyqtgraph,jlombacher/pyqtgraph,ddamiani/pyqtgraph,onlyjus/pyqtgraph,meganbkratz/acq4,JenSte/pyqtgraph,mgraupe/acq4,pbmanis/acq4,benvermaercke/pyqtgraph,welshjf/pyqtgraph,benvermaercke/pyqtgraph,benvermaercke/pyqtgraph,pbmanis/acq4,campagnola/acq4,ericdill/pyqtgraph,vallsv/pyqtgraph,campagnola/acq4,onlyjus/pyqtgraph,stscieisenhamer/pyqtgraph,nmearl/pyqtgraph,petebachant/pyqtgraph,nmearl/pyqtgraph,meganbkratz/acq4,meganbkratz/acq4,wonkoderverstaendige/MausverPyler,tropp/acq4,acq4/acq4,ericdill/pyqtgraph,gvalentine/pyqtgraph,hiuwo/acq4,mgraupe/acq4,ng110/pyqtgraph,JenSte/pyqtgraph