python学习之 argparse

官方文档：https://docs.python.org/2/library/argparse.html

本文主要内容来自官方文档（即上面的链接）。本文主要说明了一件事：argparse是用来干什么的。

argparse干了什么？

• 对于propositional argument(关于什么是propositional argument，请阅读官方文档)看两个例子

• import argparse
  parser = argparse.ArgumentParser()
  parser.add_argument("echo")
  args = parser.parse_args()
  print args.foo

  

  
  

• import argparse
  parser = argparse.ArgumentParser()
  parser.add_argument("square", help="display a square of a given number")
  args = parser.parse_args()
  print args.square**2
  

  这两个例子说明，argparse对于propositional argument其实是把命令行参数中合适的参数赋值给了我们指定的参数，比如args.square得到了我们指定的int，而上面的echo得到了我们给定的字符串

• 
  
  

  Optional arguments

  So far we, have been playing with positional arguments. Let us have a look on how to add optional ones:

  import argparse
  parser = argparse.ArgumentParser()
  parser.add_argument("--verbosity", help="increase output verbosity")
  args = parser.parse_args()
  if args.verbosity:
      print "verbosity turned on"
  print args.verbosity
  

说明optional argument 和 propositional argument的意义是一样的，只是optional arguemnt在参数后面的值会被赋予给args.verbosity

关于action关键字：

import argparse
parser = argparse.ArgumentParser()
parser.add_argument("--verbose", help="increase output verbosity",
                    action="store_true")
args = parser.parse_args()
if args.verbose:
   print "verbosity turned on"

 the value "store_true" . This means that, if the option is specified, assign the value  True  to  args.verbose . Not specifying it implies  False .

   Short options

If you are familiar with command line usage, you will notice that I haven’t yet touched on the topic of short versions of the options. It’s quite simple:

import argparse
parser = argparse.ArgumentParser()
parser.add_argument("-v", "--verbose", help="increase output verbosity",
                    action="store_true")
args = parser.parse_args()
if args.verbose:
    print "verbosity turned on"

And here goes:

$ python prog.py -v
verbosity turned on
$ python prog.py --help
usage: prog.py [-h] [-v]

optional arguments:
  -h, --help     show this help message and exit
  -v, --verbose  increase output verbosity

Note that the new ability is also reflected in the help text.

   Combining Positional and Optional arguments

Our program keeps growing in complexity:

import argparse
parser = argparse.ArgumentParser()
parser.add_argument("square", type=int,
                    help="display a square of a given number")
parser.add_argument("-v", "--verbose", action="store_true",
                    help="increase output verbosity")
args = parser.parse_args()
answer = args.square**2
if args.verbose:
    print "the square of {} equals {}".format(args.square, answer)
else:
    print answer

And now the output:

$ python prog.py
usage: prog.py [-h] [-v] square
prog.py: error: the following arguments are required: square
$ python prog.py 4
16
$ python prog.py 4 --verbose
the square of 4 equals 16
$ python prog.py --verbose 4
the square of 4 equals 16

• We’ve brought back a positional argument, hence the complaint.
• Note that the order does not matter.