Warning comes out in pip9 series
$ pip -V
pip 9.0.1
$ pip list
DEPRECATION: The default format will switch to columns in the future. You can use --format=(legacy|columns) (or define a format=(legacy|columns) in your pip.conf under the [list] section) to disable this warning.
Flask (0.12)
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Correspondence contents https://pip.pypa.io/en/stable/user_guide/#config-file
$ vi ~/.pip/pip.conf
[list]
format = columns
$ pip list
Package Version
-------- --------
Flask 0.12
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