Ability to check if string is a valid unit (in any unit system)

[langmm]

• unyt version: 1.0.4
• Python version: 2.7-3.6
• Operating System: MacOSX

Description

It would be awesome to be able to check if a string is a valid unit by something like:

if 'something' in ureg:
    ...

What I Did

Currently, you can get this by using try, except, but it would be useful out-of-the-box in a more pythonic way.

def is_unit(unit_string):
    try:
        unyt.Unit(ustr)
    except unyt.exceptions.UnitParseError:
        return False
    return True