python - getopt() not enforcing required arguments? -

i'm having problems getopt() code in script i'm writing simple file manipulation given 2 required parameters (input filename , output filename) and/or 2 optional/situational arguments (debug or help).

code is:

def main(argv):     try:         opts, args = getopt.getopt(argv, "i:o:dh", ["input-file=", "output-file=", "debug", "help"])     except getopt.getopterror:         usage()         sys.exit(2)      opt, arg in opts:         if opt in ("-h", "--help"):             usage()             sys.exit()         elif opt in ("-d", "--debug"):             global _debug             _debug = 1         elif opt in ("-i", "--input-file"):             u_input_file_name = arg         elif opt in ("-o", "--output-file"):             u_output_file_name = arg 

according getopt() documentation:

options require argument followed colon (':'; i.e., same format unix getopt() uses).

the problem understand it, variables/args followed : should enforced required ... options i , o not being enforced. running snippet garners error u_input_file_name being referenced before being assigned:

[tdelane@fbsd81-1 ~/python]$ ./inco_add_cm_mpscli.py -o google traceback (most recent call last):   file "./inco_add_cm_mpscli.py", line 57, in <module>     main(sys.argv[1:])   file "./inco_add_cm_mpscli.py", line 25, in main     infile = open(u_input_file_name, 'r') unboundlocalerror: local variable 'u_input_file_name' referenced before assignment 

what doing wrong?

an option followed colon means needs argument. doesn't mean option enforced. should write own code enforce existence of options/arguments.