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author Jeff Hammel <k0scist@gmail.com>
date Sun, 19 Feb 2017 21:05:55 -0800
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1 CommandParser
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2 =============
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4 change objects to OptionParser instances via reflection
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5
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6 Overview
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7 --------
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8
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9 It is a common pattern for command line interfaces to use subcomands (e.g.):
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10
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11 hg commit -m 'foo bar'
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12 git push origin master
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13
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14 CommandParser does this via introspection of a given class. When
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15 invoked with a class, CommandParser uses the inspect module to pull
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16 out the mandatory and optional arguments for each of the class's
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17 methods, which are translated to subcommands, and make a OptionParser
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18 instance from them. ``%prog help`` will then display all of the
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19 subcommands and ``%prog help <subcommand>`` will give you help on the
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20 ``<subcommand>`` chosen. Methods beginning with an underscore (`_`)
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21 are passed over. This gives an easy way to translate an API class
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22 into a command line program::
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23
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24 class Foo(object):
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25 """silly class that does nothing"""
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26 def __init__(self): pass
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27 def foo(self, value):
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28 print "The value is %s" % value
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29 def bar(self, fleem, verbose=False):
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30 """
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31 The good ole `bar` command
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32 - fleem: you know, that thing fleem
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33 - verbose: whether to print out more things or not
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34 """
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35 if verbose:
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36 print "You gave fleem=%s" % fleem
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37 return fleem * 2
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38
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39 import commandparser
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40 parser = commandparser.CommandParser(Foo)
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41 parser.invoke()
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42
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43 (From http://k0s.org/hg/CommandParser/file/tip/tests/simpleexample.py )
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44
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45 Example invocation::
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46
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47 (paint)│./simpleexample.py help
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48 Usage: simpleexample.py [options] command [command-options]
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49
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50 silly class that does nothing
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51
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52 Options:
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53 -h, --help show this help message and exit
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54
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55 Commands:
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56 bar The good ole `bar` command
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57 foo
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58 help print help for a given command
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59 (paint)│./simpleexample.py foo
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60 Usage: simpleexample.py foo <value>
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61
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62 simpleexample.py: error: Not enough arguments given
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63 (paint)│./simpleexample.py foo 4
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64 The value is 4
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65 (paint)│./simpleexample.py bar blah
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66 blahblah
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67
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68 For optional arguments, the type of the default value will be
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69 inspected from the function signature. Currently, mandatory arguments
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70 are all strings, though this is clearly a shortcoming.
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71
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72 The class docstring is used for ``%prog --help`` (and ``%prog help``,
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73 same thing). The method docstrings (including those of ``__init__``
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74 for global options) are used for subcommand help. If the arguments
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75 are listed in the docstring in the form given above
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76 (``- <argument> : <something about the argument``) then these are used
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77 to provide help on the individual options. Otherwise, these are left
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78 blank.
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79
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80 For straight-forward cases, it may be enough to pass your class
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81 directly to the CommandParser constructor. For more complex cases, it
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82 is an advisable pattern to create a new class (either via subclassing
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83 or e.g. rolling from scratch, as applicable) that is more amenable to
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84 CommandParser rather than modifying an (e.g.) API class to fit what
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85 CommandParser expects. This allows the use of an object-oriented
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86 interface for subcommands without sacrificing your API class, and if
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87 you can subclass then there's really not much extra code to write.
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88
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89 See http://k0s.org/hg/CommandParser/file/tip/tests for tests and examples.
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90
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92 Reference
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93 ---------
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95 * https://pypi.python.org/pypi/clime/ is a similar effort
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96
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97
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98 ----
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100 Jeff Hammel
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101
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102 http://k0s.org/hg/CommandParser
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103