One of the most common patterns with command line programs is the need to print lists of data. cliff provides a base class for commands of this type so that they only need to prepare the data, and the user can choose from one of several output formatter plugins to see the list of data in their preferred format.
The cliff.lister.Lister base class API extends Command to allow take_action() to return data to be formatted using a user-selectable formatter. Subclasses should provide a take_action() implementation that returns a two member tuple containing a tuple with the names of the columns in the dataset and an iterable that will yield the data to be output. See the description of the files command in the demoapp for details.
cliff is delivered with two output formatters for list commands. Lister adds a command line switch to let the user specify the formatter they want, so you don’t have to do any extra work in your application.
The csv formatter produces a comma-separated-values document as output. CSV data can be imported into a database or spreadsheet for further manipulation.
(.venv)$ cliffdemo files -f csv
"Name","Size"
"build",136
"cliffdemo.log",2690
"Makefile",5569
"source",408
The table formatter uses PrettyTable to produce output formatted for human consumption.
(.venv)$ cliffdemo files
+---------------+------+
| Name | Size |
+---------------+------+
| build | 136 |
| cliffdemo.log | 2546 |
| Makefile | 5569 |
| source | 408 |
+---------------+------+
The value formatter produces a space separated output with no headers.
(.venv)$ cliffdemo files -f value
build 136
cliffdemo.log 2690
Makefile 5569
source 408
This format can be very convenient when you want to pipe the output to a script.
(.venv)$ cliffdemo files -f value | while read NAME SIZE
do
echo $NAME is $SIZE bytes
done
build is 136 bytes
cliffdemo.log is 2690 bytes
Makefile is 5569 bytes
source is 408 bytes
The yaml formatter uses PyYAML to produce a YAML sequence of mappings.
(.venv)$ cliffdemo files -f yaml
- Name: dist
Size: 4096
- Name: cliffdemo.egg-info
Size: 4096
- Name: README.rst
Size: 960
- Name: setup.py
Size: 1807
- Name: build
Size: 4096
- Name: cliffdemo
Size: 4096
The json formatter produces an array of objects in indented JSON format.
(.venv)$ cliffdemo files -f json
[
{
"Name": "source",
"Size": 4096
},
{
"Name": "Makefile",
"Size": 5569
},
{
"Name": "build",
"Size": 4096
}
]
A formatter using tablib to produce HTML is available as part of cliff-tablib.
If the standard formatters do not meet your needs, you can bundle another formatter with your program by subclassing from cliff.formatters.base.ListFormatter and registering the plugin in the cliff.formatter.list namespace.