def mass_fractions(atoms, MW=None):
    r'''Calculates the mass fractions of each element in a compound,
    given a dictionary of its atoms and their counts, in the format
    {symbol: count}.

    .. math::
        w_i =  \frac{n_i MW_i}{\sum_i n_i MW_i}

    Parameters
    ----------
    atoms : dict
        dictionary of counts of individual atoms, indexed by symbol with
        proper capitalization, [-]
    MW : float, optional
        Molecular weight, [g/mol]

    Returns
    -------
    mfracs : dict
        dictionary of mass fractions of individual atoms, indexed by symbol
        with proper capitalization, [-]

    Notes
    -----
    Molecular weight is optional, but speeds up the calculation slightly. It
    is calculated using the function `molecular_weight` if not specified.

    Elemental data is from rdkit, with CAS numbers added. An exception is
    raised if an incorrect element symbol is given. Elements up to 118 are
    supported.

    Examples
    --------
    >>> mass_fractions({'H': 12, 'C': 20, 'O': 5})
    {'H': 0.03639798802478244, 'C': 0.7228692758981262, 'O': 0.24073273607709128}

    References
    ----------
    .. [1] RDKit: Open-source cheminformatics; http://www.rdkit.org
    '''
    if not MW:
        MW = molecular_weight(atoms)
    mfracs = {}
    for i in atoms:
        if i in periodic_table:
            mfracs[i] = periodic_table[i].MW*atoms[i]/MW
        else:
            raise Exception('Molecule includes unknown atoms')
    return mfracs
def mass_fractions(atoms, MW=None):
    r'''Calculates the mass fractions of each element in a compound,
    given a dictionary of its atoms and their counts, in the format
    {symbol: count}.

    .. math::
        w_i =  \frac{n_i MW_i}{\sum_i n_i MW_i}

    Parameters
    ----------
    atoms : dict
        dictionary of counts of individual atoms, indexed by symbol with
        proper capitalization, [-]
    MW : float, optional
        Molecular weight, [g/mol]

    Returns
    -------
    mfracs : dict
        dictionary of mass fractions of individual atoms, indexed by symbol
        with proper capitalization, [-]

    Notes
    -----
    Molecular weight is optional, but speeds up the calculation slightly. It
    is calculated using the function `molecular_weight` if not specified.

    Elemental data is from rdkit, with CAS numbers added. An exception is
    raised if an incorrect element symbol is given. Elements up to 118 are
    supported.

    Examples
    --------
    >>> mass_fractions({'H': 12, 'C': 20, 'O': 5})
    {'H': 0.03639798802478244, 'C': 0.7228692758981262, 'O': 0.24073273607709128}

    References
    ----------
    .. [1] RDKit: Open-source cheminformatics; http://www.rdkit.org
    '''
    if not MW:
        MW = molecular_weight(atoms)
    mfracs = {}
    for i in atoms:
        if i in periodic_table:
            mfracs[i] = periodic_table[i].MW*atoms[i]/MW
        else:
            raise Exception('Molecule includes unknown atoms')
    return mfracs
def mass_fractions ( atoms , MW = None ) : if not MW : MW = molecular_weight ( atoms ) mfracs = { } for i in atoms : if i in periodic_table : mfracs [ i ] = periodic_table [ i ] . MW * atoms [ i ] / MW else : raise Exception ( 'Molecule includes unknown atoms' ) return mfracs
r'''Calculates the mass fractions of each element in a compound,
    given a dictionary of its atoms and their counts, in the format
    {symbol: count}.

    .. math::
        w_i =  \frac{n_i MW_i}{\sum_i n_i MW_i}

    Parameters
    ----------
    atoms : dict
        dictionary of counts of individual atoms, indexed by symbol with
        proper capitalization, [-]
    MW : float, optional
        Molecular weight, [g/mol]

    Returns
    -------
    mfracs : dict
        dictionary of mass fractions of individual atoms, indexed by symbol
        with proper capitalization, [-]

    Notes
    -----
    Molecular weight is optional, but speeds up the calculation slightly. It
    is calculated using the function `molecular_weight` if not specified.

    Elemental data is from rdkit, with CAS numbers added. An exception is
    raised if an incorrect element symbol is given. Elements up to 118 are
    supported.

    Examples
    --------
    >>> mass_fractions({'H': 12, 'C': 20, 'O': 5})
    {'H': 0.03639798802478244, 'C': 0.7228692758981262, 'O': 0.24073273607709128}

    References
    ----------
    .. [1] RDKit: Open-source cheminformatics; http://www.rdkit.org
r Calculates the mass fractions of each element in a compound given a dictionary of its atoms and their counts in the format { symbol : count } .