Python command-line parsing tool argparse module "4"

In the previous section we explained the Add_argument () method, which we will learn about the Parse_args () method. The function of the Parse_args () method is to parse the command-line arguments and return the parsed namespace. By default, the parameters are obtained from the SYS.ARGV.      1. Parameter value SyntaxParse_args () supports a variety of syntax to parse parameters, the simplest way to do so is to pass parameters and values separately

>>> parser = Argparse. Argumentparser (prog='PROG')>>> Parser.add_argument ('- x')>>> Parser.add_argument ('--foo')>>> Parser.parse_args ('- X ×'. Split ()) Namespace (foo=none, x='X')>>> Parser.parse_args ('--foo Foo'. Split ()) Namespace (foo='FOO', X=none)

    For comparing long parameters with values, you can use = to pass

>>> Parser.parse_args ('--foo=foo'. Split ()) Namespace (foo='  FOO', X=none)

For simple parameters, parameters and values can be linked together

>>> Parser.parse_args ('-xx'. Split ()) Namespace (foo=none, x='  X')

    Several simple parameters can also be linked together, using only one-as long as the last parameter only needs a value of the case is established.

>>> parser = Argparse. Argumentparser (prog='PROG')>>> Parser.add_argument ('- x', action='store_true')>>> Parser.add_argument ('- y', action='store_true')>>> Parser.add_argument ('- Z')>>> Parser.parse_args ('-xyzz'. Split ()) Namespace (x=true, Y=true, z='Z')

   2. Non-legal parameters

Error when passing an illegal parameter, and exit return usage example

>>> parser = Argparse. Argumentparser (prog='PROG')>>> Parser.add_argument ('--foo', type=int)>>> Parser.add_argument ('Bar', nargs='?') >>>#Invalid type>>> Parser.parse_args (['--foo','spam']) Usage:prog [-h] [--Foo Foo] [Bar] PROG:error:argument--foo:invalid int Value:'spam'>>>#Invalid option>>> Parser.parse_args (['--bar']) Usage:prog [-h] [--Foo Foo] [Bar] PROG:error:no such option:--Bar>>>#wrong number of arguments>>> Parser.parse_args (['spam','Badger']) Usage:prog [-h] [--Foo Foo] [Bar] PROG:error:extra arguments Found:badger

3. Included-parametersIf the parameters contain--words, it is easy to cause ambiguity.

>>> parser = Argparse. Argumentparser (prog='PROG')>>> Parser.add_argument ('- x')>>> Parser.add_argument ('Foo', nargs='?') >>>#no negative number options, so-1 is a positional argument>>> Parser.parse_args (['- x','-1']) Namespace (foo=none, x='-1') >>>#no negative number options, So-1 and-5 is positional arguments>>> Parser.parse_args (['- x','-1','-5']) Namespace (foo='-5', x='-1') >>> parser = Argparse. Argumentparser (prog='PROG')>>> Parser.add_argument ('-1', dest=' One')>>> Parser.add_argument ('Foo', nargs='?') >>>#negative number options present, so-1 is an option>>> Parser.parse_args (['-1','X']) Namespace (foo=none, one='X') >>>#negative number options present, so-2 is an option>>> Parser.parse_args (['-2']) Usage:prog [-h] [-1One ] [Foo] PROG:error:no such option:-2 >>>#negative number options present, so both-1s is options>>> Parser.parse_args (['-1','-1']) Usage:prog [-h] [-1One ] [Foo] PROG:error:argument-1:expected one argument

    If you use a positional parameter that must precede the-prefix, and it does not look like a negative number, you can insert it at this point--to tell the argument behind the parser to be the positional parameter.

>>> Parser.parse_args (['---'-f']) Namespace ( Foo='-f', One=none)

 4. Parameter name abbreviation

The Parse_args () method allows long parameters to be abbreviated as long as there is no ambiguity.

>>> parser = Argparse. Argumentparser (prog='PROG')>>> Parser.add_argument ('-bacon')>>> Parser.add_argument ('-badger')>>> Parser.parse_args ('-bac MMM'. Split ()) Namespace (Bacon='MMM', badger=None)>>> Parser.parse_args ('-bad WOOD'. Split ()) Namespace (Bacon=none, badger='WOOD')>>> Parser.parse_args ('-ba BA'. Split ()) Usage:prog [-h] [-bacon bacon] [-Badger Badger] PROG:error:ambiguous option:-ba could Match-badger,-bacon

     5. Do not use SYS.ARGVIn addition to using SYS.ARGV to pass parameters, you can use a string list to pass parameters.

>>> parser =Argparse. Argumentparser ()>>>parser.add_argument ( ...'integers', metavar='int', Type=int, Choices=xrange (10),... Nargs='+', help='An integer in the range 0..9')>>>parser.add_argument ( ...'--sum', dest='Accumulate', action='Store_const', const=sum,... default=max, help='sum the integers (default:find the max)')>>> Parser.parse_args (['1','2','3','4']) Namespace (accumulate=<built-inchfunction Max>, integers=[1, 2, 3, 4])>>> Parser.parse_args ('1 2 3 4--sum'. Split ()) Namespace (Accumulate=<built-inchfunction Sum>, integers=[1, 2, 3, 4])

 6. Customizing the namespace

Sometimes you do not need to create a new namespace, you can pass a namespace directly.

>>>classC (object): ...Pass...>>> C =C ()>>> parser =Argparse. Argumentparser ()>>> Parser.add_argument ('--foo')>>> Parser.parse_args (args=['--foo','BAR'], namespace=c)>>>C.foo'BAR'

Python command-line parsing tool argparse module "4"