matplotlib - Python: function with list of arguments of variable length -

i'm trying plot (on same figure) data excel sheet, , want input variable length list of strings, corresponding different materials. following error: typeerror: 'nonetype' object not iterable don't understand why. here code:

import xlrd import matplotlib.pyplot  plt numpy import * def transmittance(*glass):     wb=xlrd.open_workbook('schott_optical_glass_catalogue_excel_december_2012.xls')     sheet1=wb.sheet_by_index(0)     transm_index=[]  #lista vuota     plt.figure(1)     plt.xlabel('wavelength $\lambda$[nm]')     plt.ylabel('transmittance')     item in glass:         in range(sheet1.nrows):             if sheet1.cell_value(i,0)==glass:                 reversed_transmission=sheet1.row_values(i,37,67)                 transm_index=reversed_transmission[::-1]                 new_transm_index=[float(ni)  ni in transm_index ]     wavel_range=sheet1.row_values(3,37,67)     temp_wavel= [k.split('/')[1] k in wavel_range]     wrange=map(int,temp_wavel[::-1])     plt.plot(wrange,new_transm_index, 'r-')     plt.grid(true, which="both")     plt.show()     return new_transm_index, wrange  if __name__=='__main__':     new_transm_index=transmittance('n-basf64','n-bk7')     print 'get tuple length , glass name: ' ,new_transm_index 

i not reproduce typeerror describe in question (which if called transmittance() without parameters). however, 2 different errors instead, when calling function xls file of same name found via google.

• you iterate items in glass, compare whole list instead of current item
• when create new_transm_index list, can't cast float, there empty strings in table; in case assume value zero.

finally, if want new_transm_index hold list each item glass (as described in comment), should use dictionary, mapping items (keys) respective lists (values).

... new_transm_index = {} # create dictionary item in glass:     in range(sheet1.nrows):         if sheet1.cell_value(i, 0) == item: # compare item, not list             ...             # not cast ' ' float, use 0 if not of type float             new_transm_index[item] = [ni if type(ni) == float else 0 ni in transm_index] ... item in glass: # add plots items common diagram     plt.plot(wrange,new_transm_index[item]) plt.grid(true, which="both") plt.show() ...