def METHOD_NAME(key):
    """
    Retrieve a constant by key. This is just a short cut into a dictionary.
    Parameters
    ----------
    key : `str`
        Key in dictionary in ``constants``.
    Returns
    -------
    constant : `~astropy.constants.Constant`
    See Also
    --------
    `~sunpy.sun.constants` :
        Contains the description of ``constants``, which, as a dictionary literal object, does not
        itself possess a docstring.
    Examples
    --------
    >>> from sunpy.sun import constants
    >>> constants.get('mass')
    <<class 'astropy.constants.iau2015.IAU2015'> name='Solar mass' value=1.9884754153381438e+30 uncertainty=9.236140093538353e+25 unit='kg' reference='IAU 2015 Resolution B 3 + CODATA 2014'>
    """
    ret = constants[key]
    ret.__doc__ = ret.name
    return ret