Break up arguments section (#2586)

Author: Rowlando13

docs/arguments.rst

@@ -5,195 +5,118 @@ Arguments
 
 .. currentmodule:: click
 
-Arguments work similarly to :ref:`options <options>` but are positional.
-They also only support a subset of the features of options due to their
-syntactical nature. Click will also not attempt to document arguments for
-you and wants you to :ref:`document them manually <documenting-arguments>`
-in order to avoid ugly help pages.
+Arguments are:
+
+*   Are positional in nature.
+*   Similar to a limited version of :ref:`options <options>` that can take an arbitrary number of inputs
+*   :ref:`Documented manually <documenting-arguments>`.
+
+Useful and often used kwargs are:
+
+*   ``default``: Passes a default.
+*   ``nargs``: Sets the number of arguments. Set to -1 to take an arbitrary number.
 
 Basic Arguments
 ---------------
 
-The most basic option is a simple string argument of one value.  If no
-type is provided, the type of the default value is used, and if no default
-value is provided, the type is assumed to be :data:`STRING`.
+A minimal :class:`click.Argument` solely takes one string argument: the name of the argument. This will assume the argument is required, has no default, and is of the type ``str``.
 
 Example:
 
 .. click:example::
 
     @click.command()
     @click.argument('filename')
-    def touch(filename):
+    def touch(filename: str):
         """Print FILENAME."""
         click.echo(filename)
 
-And what it looks like:
+And from the command line:
 
 .. click:run::
 
     invoke(touch, args=['foo.txt'])
 
-Variadic Arguments
-------------------
 
-The second most common version is variadic arguments where a specific (or
-unlimited) number of arguments is accepted.  This can be controlled with
-the ``nargs`` parameter.  If it is set to ``-1``, then an unlimited number
-of arguments is accepted.
+An argument may be assigned a :ref:`parameter type <parameter-types>`. If no type is provided, the type of the default value is used. If no default value is provided, the type is assumed to be :data:`STRING`.
 
-The value is then passed as a tuple.  Note that only one argument can be
-set to ``nargs=-1``, as it will eat up all arguments.
+.. admonition:: Note on Required Arguments
 
-Example:
+   It is possible to make an argument required by setting ``required=True``.  It is not recommended since we think command line tools should gracefully degrade into becoming no ops.  We think this because command line tools are often invoked with wildcard inputs and they should not error out if the wildcard is empty.
+
+Multiple Arguments
+-----------------------------------
+
+To set the number of argument use the ``nargs`` kwarg. It can be set to any positive integer and -1. Setting it to -1, makes the number of arguments arbitrary (which is called variadic) and can only be used once. The arguments are then packed as a tuple and passed to the function.
 
 .. click:example::
 
     @click.command()
-    @click.argument('src', nargs=-1)
-    @click.argument('dst', nargs=1)
-    def copy(src, dst):
+    @click.argument('src', nargs=1)
+    @click.argument('dsts', nargs=-1)
+    def copy(src: str, dsts: tuple[str, ...]):
         """Move file SRC to DST."""
-        for fn in src:
-            click.echo(f"move {fn} to folder {dst}")
+        for destination in dsts:
+            click.echo(f"Copy {src} to folder {destination}")
 
-And what it looks like:
+And from the command line:
 
 .. click:run::
 
-    invoke(copy, args=['foo.txt', 'bar.txt', 'my_folder'])
-
-Note that this is not how you would write this application.  The reason
-for this is that in this particular example the arguments are defined as
-strings.  Filenames, however, are not strings!  They might be on certain
-operating systems, but not necessarily on all.  For better ways to write
-this, see the next sections.
+    invoke(copy, args=['foo.txt', 'usr/david/foo.txt', 'usr/mitsuko/foo.txt'])
 
-.. admonition:: Note on Non-Empty Variadic Arguments
+.. admonition:: Note on Handling Files
 
-   If you come from ``argparse``, you might be missing support for setting
-   ``nargs`` to ``+`` to indicate that at least one argument is required.
+    This is not how you should handle files and files paths. This merely used as a simple example. See :ref:`handling-files` to learn more about how to handle files in parameters.
 
-   This is supported by setting ``required=True``.  However, this should
-   not be used if you can avoid it as we believe scripts should gracefully
-   degrade into becoming noops if a variadic argument is empty.  The
-   reason for this is that very often, scripts are invoked with wildcard
-   inputs from the command line and they should not error out if the
-   wildcard is empty.
+Argument Escape Sequences
+---------------------------
 
-.. _file-args:
+If you want to process arguments that look like options, like a file named ``-foo.txt`` or ``--foo.txt`` , you must pass the ``--`` separator first. After you pass the ``--``, you may only pass arguments. This is a common feature for POSIX command line tools.
 
-File Arguments
---------------
-
-Since all the examples have already worked with filenames, it makes sense
-to explain how to deal with files properly.  Command line tools are more
-fun if they work with files the Unix way, which is to accept ``-`` as a
-special file that refers to stdin/stdout.
-
-Click supports this through the :class:`click.File` type which
-intelligently handles files for you.  It also deals with Unicode and bytes
-correctly for all versions of Python so your script stays very portable.
-
-Example:
+Example usage:
 
 .. click:example::
 
     @click.command()
-    @click.argument('input', type=click.File('rb'))
-    @click.argument('output', type=click.File('wb'))
-    def inout(input, output):
-        """Copy contents of INPUT to OUTPUT."""
-        while True:
-            chunk = input.read(1024)
-            if not chunk:
-                break
-            output.write(chunk)
-
-And what it does:
-
-.. click:run::
+    @click.argument('files', nargs=-1, type=click.Path())
+    def touch(files):
+        """Print all FILES file names."""
+        for filename in files:
+            click.echo(filename)
 
-    with isolated_filesystem():
-        invoke(inout, args=['-', 'hello.txt'], input=['hello'],
-               terminate_input=True)
-        invoke(inout, args=['hello.txt', '-'])
+And from the command line:
 
-File Path Arguments
--------------------
+.. click:run::
 
-In the previous example, the files were opened immediately.  But what if
-we just want the filename?  The naïve way is to use the default string
-argument type. The :class:`Path` type has several checks available which raise nice
-errors if they fail, such as existence. Filenames in these error messages are formatted
-with :func:`format_filename`, so any undecodable bytes will be printed nicely.
+    invoke(touch, ['--', '-foo.txt', 'bar.txt'])
 
-Example:
+If you don't like the ``--`` marker, you can set ignore_unknown_options to True to avoid checking unknown options:
 
 .. click:example::
 
-    @click.command()
-    @click.argument('filename', type=click.Path(exists=True))
-    def touch(filename):
-        """Print FILENAME if the file exists."""
-        click.echo(click.format_filename(filename))
+    @click.command(context_settings={"ignore_unknown_options": True})
+    @click.argument('files', nargs=-1, type=click.Path())
+    def touch(files):
+        """Print all FILES file names."""
+        for filename in files:
+            click.echo(filename)
 
-And what it does:
+And from the command line:
 
 .. click:run::
 
-    with isolated_filesystem():
-        with open('hello.txt', 'w') as f:
-            f.write('Hello World!\n')
-        invoke(touch, args=['hello.txt'])
-        println()
-        invoke(touch, args=['missing.txt'])
-
-
-File Opening Safety
--------------------
-
-The :class:`FileType` type has one problem it needs to deal with, and that
-is to decide when to open a file.  The default behavior is to be
-"intelligent" about it.  What this means is that it will open stdin/stdout
-and files opened for reading immediately.  This will give the user direct
-feedback when a file cannot be opened, but it will only open files
-for writing the first time an IO operation is performed by automatically
-wrapping the file in a special wrapper.
-
-This behavior can be forced by passing ``lazy=True`` or ``lazy=False`` to
-the constructor.  If the file is opened lazily, it will fail its first IO
-operation by raising an :exc:`FileError`.
-
-Since files opened for writing will typically immediately empty the file,
-the lazy mode should only be disabled if the developer is absolutely sure
-that this is intended behavior.
-
-Forcing lazy mode is also very useful to avoid resource handling
-confusion.  If a file is opened in lazy mode, it will receive a
-``close_intelligently`` method that can help figure out if the file
-needs closing or not.  This is not needed for parameters, but is
-necessary for manually prompting with the :func:`prompt` function as you
-do not know if a stream like stdout was opened (which was already open
-before) or a real file that needs closing.
-
-Starting with Click 2.0, it is also possible to open files in atomic mode by
-passing ``atomic=True``.  In atomic mode, all writes go into a separate
-file in the same folder, and upon completion, the file will be moved over to
-the original location.  This is useful if a file regularly read by other
-users is modified.
+    invoke(touch, ['-foo.txt', 'bar.txt'])
 
 
 .. _environment-variables:
 
 Environment Variables
 ---------------------
 
-Like options, arguments can also grab values from an environment variable.
-Unlike options, however, this is only supported for explicitly named
-environment variables.
+Arguments can use environment variables. To do so, pass the name(s) of the environment variable(s) via `envvar` in ``click.argument``.
 
-Example usage:
+Checking one environment variable:
 
 .. click:example::
 
@@ -208,59 +131,28 @@ And from the command line:
 .. click:run::
 
     with isolated_filesystem():
+        # Writing the file in the filesystem.
         with open('hello.txt', 'w') as f:
             f.write('Hello World!')
         invoke(echo, env={'SRC': 'hello.txt'})
 
-In that case, it can also be a list of different environment variables
-where the first one is picked.
-
-Generally, this feature is not recommended because it can cause the user
-a lot of confusion.
-
-Option-Like Arguments
----------------------
 
-Sometimes, you want to process arguments that look like options.  For
-instance, imagine you have a file named ``-foo.txt``.  If you pass this as
-an argument in this manner, Click will treat it as an option.
-
-To solve this, Click does what any POSIX style command line script does,
-and that is to accept the string ``--`` as a separator for options and
-arguments.  After the ``--`` marker, all further parameters are accepted as
-arguments.
-
-Example usage:
+Checking multiple environment variables:
 
 .. click:example::
 
     @click.command()
-    @click.argument('files', nargs=-1, type=click.Path())
-    def touch(files):
-        """Print all FILES file names."""
-        for filename in files:
-            click.echo(filename)
-
-And from the command line:
-
-.. click:run::
-
-    invoke(touch, ['--', '-foo.txt', 'bar.txt'])
-
-If you don't like the ``--`` marker, you can set ignore_unknown_options to
-True to avoid checking unknown options:
-
-.. click:example::
-
-    @click.command(context_settings={"ignore_unknown_options": True})
-    @click.argument('files', nargs=-1, type=click.Path())
-    def touch(files):
-        """Print all FILES file names."""
-        for filename in files:
-            click.echo(filename)
+    @click.argument('src', envvar=['SRC', 'SRC_2'], type=click.File('r'))
+    def echo(src):
+        """Print value of SRC environment variable."""
+        click.echo(src.read())
 
 And from the command line:
 
 .. click:run::
 
-    invoke(touch, ['-foo.txt', 'bar.txt'])
+    with isolated_filesystem():
+        # Writing the file in the filesystem.
+        with open('hello.txt', 'w') as f:
+            f.write('Hello World from second variable!')
+        invoke(echo, env={'SRC_2': 'hello.txt'})