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Python/Libs/CLI/click.md

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+# [Click](https://click.palletsprojects.com) Lib
+
+## Command Creation
+
+```py
+import click
+
+# the decorator converts the function into a Command which then can be invoked
+@click.command()
+def hello():
+    click.echo('Hello World!')
+
+if __name__ == '__main__':
+    hello()
+```
+
+### Nesting Commands
+
+Commands can be attached to other commands of type `Group`. This allows arbitrary nesting of scripts. As an example here is a script that implements two commands for managing databases:
+
+```py
+@click.group()
+def cli():
+    pass
+
+@click.command()
+def initdb():
+    click.echo('Initialized the database')
+
+@click.command()
+def dropdb():
+    click.echo('Dropped the database')
+
+cli.add_command(initdb)
+cli.add_command(dropdb)
+```
+
+The `group()` decorator works like the `command()` decorator, but creates a Group object instead which can be given multiple subcommands that can be attached with `Group.add_command()`.
+
+For simple scripts, it’s also possible to automatically attach and create a command by using the `Group.command()` decorator instead.  
+The above script can instead be written like this:
+
+```py
+@click.group()
+def cli():
+    pass
+
+@cli.command()
+def initdb():
+    click.echo('Initialized the database')
+
+@cli.command()
+def dropdb():
+    click.echo('Dropped the database')
+```
+
+You would then invoke the Group in your setuptools entry points or other invocations:
+
+```py
+if __name__ == '__main__':
+    cli()
+```
+
+### Adding Parameters
+
+To add parameters, use the `option()` and `argument()` decorators:
+
+```py
+@click.command()
+@click.option('--count', default=1, help='number of greetings')
+@click.argument('name')
+def hello(count, name):
+    for x in range(count):
+        click.echo(f'Hello {name}!')
+```