import pylab
from pylab import rcParams
figsize=(80./25.4,80./25.4)
rcParams["figure.figsize"]=figsize
figsize=rcParams["figure.figsize"]

def try_figsize(figsize=(80/25.4, 80/25.4)):
    print "desired figsize:", figsize
    pylab.close("all")
    pylab.figure(1,figsize=figsize)
    print "actual figsize:", pylab.gcf().get_size_inches()



try_figsize()
pylab.savefig("figsize-1.png")
pylab.show()
try_figsize()
pylab.savefig("figsize-2.png")