fix for python 2.4
fix for python 2.4

tectronics/pcaspy,mscheng/pcaspy,paulscherrerinstitute/pcaspy,paulscherrerinstitute/pcaspy,HaveF/pcaspy,HaveF/pcaspy,paulscherrerinstitute/pcaspy,mscheng/pcaspy,tectronics/pcaspy