mirror of
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116 lines
2.2 KiB
ReStructuredText
116 lines
2.2 KiB
ReStructuredText
Default values
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==============
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For elements such as arguments and options, if ``default`` property is set to a string, its value is stored in case the element was not used (if it's not a string, it'll be used as ``init`` property instead, see :ref:`actions`).
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.. code-block:: lua
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:linenos:
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parser:option("-o --output", "Output file.", "a.out")
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-- Equivalent:
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parser:option "-o" "--output"
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:description "Output file."
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:default "a.out"
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::
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$ lua script.lua
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.. code-block:: lua
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{
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output = "a.out"
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}
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The existence of a default value is reflected in help message, unless ``show_default`` property is set to ``false``.
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::
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$ lua script.lua --help
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::
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Usage: script.lua [-o <output>] [-h]
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Options:
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-o <output>, --output <output>
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Output file. (default: a.out)
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-h, --help Show this help message and exit.
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Note that invocation without required arguments is still an error.
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::
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$ lua script.lua -o
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::
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Usage: script.lua [-o <output>] [-h]
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Error: too few arguments
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Default mode
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------------
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``defmode`` property regulates how argparse should use the default value of an element.
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If ``defmode`` contains ``u`` (for unused), the default value will be automatically passed to the element if it was not invoked at all. This is the default behavior.
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If ``defmode`` contains ``a`` (for argument), the default value will be automatically passed to the element if not enough arguments were passed, or not enough invocations were made.
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Consider the difference:
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.. code-block:: lua
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:linenos:
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parser:option "-o"
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:default "a.out"
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parser:option "-p"
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:default "password"
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:defmode "arg"
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::
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$ lua script.lua -h
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::
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Usage: script.lua [-o <o>] [-p [<p>]] [-h]
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Options:
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-o <o> default: a.out
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-p [<p>] default: password
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-h, --help Show this help message and exit.
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::
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$ lua script.lua
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.. code-block:: lua
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{
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o = "a.out"
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}
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::
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$ lua script.lua -p
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.. code-block:: lua
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{
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o = "a.out",
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p = "password"
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}
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::
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$ lua script.lua -o
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::
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Usage: script.lua [-o <o>] [-p [<p>]] [-h]
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Error: too few arguments
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