python - NameError: global name 'b' is not defined -

i have script wih following structure:

def func():     bfile=open(b, 'r')     cfile=open(c, 'r')     dfile=open(d, 'r')  if __name__=='__main__':     if len(sys.argv)==1:         print 'guidence'         sys.exit()     else:         opts,args=getopt.getopt(sys.argv,'b:c:d:a')         a=false         opt,arg in opts:             if opt=='-a':                 a=true             elif opt=='-b':                 b=arg             elif opt=='-c':                 c=arg             elif opt=='-d':                 d=arg         func() 

i run in way:

# python script.py -b file1 -c file1 -d file1  in func() nameerror: global name 'b' not defined 

i define global file1. no work.

update

i know problem is: result of print opts []. has not values. why?

you have 2 issues.

first, getopt stops if encounters non-option. since sys.argv[0] script name, it's non-option , parsing stops there.
want pass sys.argv[1:] getopt.

this what's causing print opts show [], , since opts empty global variables never created, complaint don't exist come from.

second, since -a wants parameter, need colon after it.

in all, should work:

opts, args = getopt.getopt(sys.argv[1:], 'b:c:d:a:') 

also, shouldn't pass parameters in globals.