This represents our best thinking about how to start your python script.
(Though you probably want to remove the excess comments).
1 #!/usr/bin/env python
2
3 # #!/usr/bin/env python - will search for the first python
4 # interpreter on your path
5 # unlike
6 # #!/usr/bin/python2.5 - which will only run if there is a file
7 # python 2.5 is installed at /usr/bin
8
9 """
10 Module doc string
11
12 if you import this module and do help (module) you'll see this
13
14 """
15 # optparse is both easy to use and produces clean code
16 # the main optparse docs can be found here:
17 # http://docs.python.org/library/optparse.html
18 # there's a much better tutorial that works you through optparse
19 # starting with a simple example and slowly adding complexity.
20 from optparse import OptionParser
21 import sys
22
23
24 # I like to make a separate function to configure the option parser
25 # I like my functions to fit with-in a single screen-full)
26
27 def make_parser():
28 """
29 Construct an option parser
30 """
31 usage = """%prog: args
32
33 this describes how to use the program
34 """
35
36 parser = OptionParser(usage)
37
38 # add_options usually takes two options, you can skip the
39 # - are one character (short) options (e.g. -h)
40 #
41 # -- are long options, the name is also used as the
42 # variable name attached that holds the option
43
44 parser.add_option('-e', '--error', help="set error code")
45
46 # opt_parse can be configured to store different kinds of values
47 # like filenames, and boolean options
48 parser.add_option('-b', '--bad-option', action="store_true",
49 help='trigger an option error')
50
51 # you can also do simple type checking on parameters
52 parser.add_option('-n', '--number', help="set a number", type="int")
53 parser.set_default(error=None,
54 bad_option=False,
55 number=0)
56 return parser
57
58 def main(cmdline=None):
59 """
60 Example main function.
61
62 If cmdline is none, parser.parse_args will look at
63 sys.argv[1:] by default
64
65 However if import this module in python call this main function
66 like this:
67
68 main(['-n', '3', 'asdf', 'jkl'])
69
70 in addition to running it from the shell.
71 """
72 parser = make_parser()
73
74 opts, args = parser.parse_args(cmdline)
75
76 if opts.error is not None:
77 return opts.error
78 elif opts.bad_option:
79 # you can call parser.error, which will show an error message
80 # displays the help, and then exits the program
81 parser.error("you called a bad option")
82
83 # args is now just a list, of everything that wasn't an
84 # "option". AKA everything that started with - or --
85 for i in range(len(args)):
86 print "arg %d: %s" % (i, args[i])
87
88 print "the number is:", opts.number
89 # opts.number is always defined, as I set a default value
90 # up in the make_parser
91
92 return 0
93
94 if __name__ == "__main__":
95 # this runs when the application is run from the command
96 # it grabs sys.argv[1:] which is everything after the program name
97 # and passes it to main
98 # the return value from main is then used as the argument to
99 # sys.exit, which you can test for in the shell.
100 # program exit codes are usually 0 for ok, and non-zero for something
101 # going wrong.
102 sys.exit(main(sys.argv[1:]))
103
104 # Try the following examples
105 # python script_template.py
106 # python script_template.py --help
107 # ./script_template.py a b c
108 # ./script_template.py --bad-option
109 # python ./script_template.py -n 4
110 # python ./script_template.py --number foo
111
112
113
114 # Guido von Rossum (inventor of python) has this write up on how to
115 # write a main
116 # http://www.artima.com/weblogs/viewpost.jsp?thread=4829
117 # however he used the older getopt module which isn't as easy
118 # to configure as optparse