I would like to calculate the max and min of many netcdf files. I know how to create one big array and then concatenate and find the numpy.max but when I run this on 1000's of arrays I have a memory error. What I would prefer is to loop through the arrays and produce the maximum without having the make a big array. My idea goes something like: netCDF_list=[] maxarray=[] for dir in glob.glob(MainFolder + '*/01/')+ glob.glob(MainFolder + '*/02/')+ glob.glob(MainFolder + '*/12/'): for ncfile in glob.glob(dir + '*.nc'): netCDF_list.append(ncfile) for filename in netCDF_list: ncfile=netCDF4.Dataset(filename) TSFC=ncfile.variables['T_SFC'][:] fillvalue=ncfile.variables['T_SFC']._FillValue TSFC=MA.masked_values(TSFC, fillvalue) for i in TSFC: if i == N.max(TSFC, axis=0): maxarray.append(i) else: pass print maxarray