How to use the quantities.constants.utils._cd function in quantities

)
atomic_unit_of_electric_field_gradient = UnitConstant(
    'atomic_unit_of_electric_field_gradient',
    _cd('atomic unit of electric field gradient'),
    symbol='(E_h/(e*a_0**2))',
    u_symbol='(E_h/(e·a₀²))'
)
atomic_unit_of_electric_polarizablity = UnitConstant(
    'atomic_unit_of_electric_polarizablity',
    _cd('atomic unit of electric polarizablity'),
    symbol='(e**2*a_0**2/E_h)',
    u_symbol='(e²·a₀²/E_h)'
)
atomic_unit_of_electric_potential = UnitConstant(
    'atomic_unit_of_electric_potential',
    _cd('atomic unit of electric potential'),
    symbol='(E_h/e)'
)
atomic_unit_of_electric_quadrupole_moment = UnitConstant(
    'atomic_unit_of_electric_quadrupole_moment',
    _cd('atomic unit of electric quadrupole moment'),
    symbol='(e*a_0**2)',
    u_symbol='(e·a₀²)'
)
atomic_unit_of_energy = UnitConstant(
    'atomic_unit_of_energy',
    _cd('atomic unit of energy'),
)
atomic_unit_of_force = UnitConstant(
    'atomic_unit_of_force',
    _cd('atomic unit of force'),
    symbol='(E_h/a_0)',

)
natural_unit_of_energy = UnitConstant(
    'natural_unit_of_energy',
    _cd('natural unit of energy'),
    symbol='(m_e*c**2)',
    u_symbol='(mₑ·c²)'
)
natural_unit_of_length = UnitConstant(
    'natural_unit_of_length',
    _cd('natural unit of length'),
    symbol='lambdabar_C',
    u_symbol='ƛ_C'
)
natural_unit_of_mass = UnitConstant(
    'natural_unit_of_mass',
    _cd('natural unit of mass'),
    symbol='m_e',
    u_symbol='mₑ'
)
natural_unit_of_momentum = UnitConstant(
    'natural_unit_of_momentum',
    _cd('natural unit of momentum'),
    symbol='(m_e*c)',
    u_symbol='(mₑ·c)'
)
natural_unit_of_time = UnitConstant(
    'natural_unit_of_time',
    _cd('natural unit of time'),
    symbol='(hbar/(m_e*c**2))',
    u_symbol='(ħ/(mₑ·c²))'
)
natural_unit_of_velocity = UnitConstant(

symbol='c'
)
g_n = neutron_g_factor = UnitConstant(
    'neutron_g_factor',
    _cd('neutron g factor'),
    symbol='g_n'
)
gamma_n = neutron_gyromagnetic_ratio = UnitConstant(
    'neutron_gyromagnetic_ratio',
    _cd('neutron gyromagnetic ratio'),
    symbol='gamma_n',
    u_symbol='γ_n'
)
neutron_gyromagnetic_ratio_over_2_pi = UnitConstant(
    'neutron_gyromagnetic_ratio_over_2_pi',
    _cd('neutron gyromagnetic ratio over 2 pi'),
    symbol='(gamma_n/(2*pi))',
    u_symbol='(γ_n/(2·π))'
)
mu_n = neutron_magnetic_moment = UnitConstant(
    'neutron_magnetic_moment',
    _cd('neutron magnetic moment'),
    symbol='mu_n',
    u_symbol='μ_n'
)
m_n = neutron_mass = UnitConstant(
    'neutron_mass',
    _cd('neutron mass'),
    symbol='m_n'
)
G = Newtonian_constant_of_gravitation = UnitConstant(
    'Newtonian_constant_of_gravitation',

'conductance_quantum',
    _cd('conductance quantum'),
    symbol='G_0',
    u_symbol='G₀'
)
K_J90 = conventional_value_of_Josephson_constant = UnitConstant(
    'conventional_value_of_Josephson_constant',
    _cd('conventional value of Josephson constant')
)
R_K90 = conventional_value_of_von_Klitzing_constant = UnitConstant(
    'conventional_value_of_von_Klitzing_constant',
    _cd('conventional value of von Klitzing constant')
)
Cu_x_unit = UnitConstant(
    'Cu_x_unit',
    _cd('Cu x unit'),
    symbol='CuKalpha_1',
    u_symbol='CuKα₁'
)
g_d = deuteron_g_factor = UnitConstant(
    'deuteron_g_factor',
    _cd('deuteron g factor'),
    symbol='g_d'
)
mu_d = deuteron_magnetic_moment = UnitConstant(
    'deuteron_magnetic_moment',
    _cd('deuteron magnetic moment'),
    symbol='mu_d',
    u_symbol='μ_d'
)
m_d = deuteron_mass = UnitConstant(
    'deuteron_mass',

)
mu_e = electron_magnetic_moment = UnitConstant(
    'electron_magnetic_moment',
    _cd('electron magnetic moment'),
    symbol='mu_e',
    u_symbol='μₑ'
)
a_e = electron_magnetic_moment_anomaly = UnitConstant(
    'electron_magnetic_moment_anomaly',
    _cd('electron magnetic moment anomaly'),
    symbol='a_e',
    u_symbol='aₑ'
)
m_e = electron_mass = UnitConstant(
    'electron_mass',
    _cd('electron mass'),
    symbol='m_e',
    u_symbol='mₑ'
)
eV = electron_volt = UnitConstant(
    'electron_volt',
    _cd('electron volt'),
    symbol='eV'
)
e = elementary_charge = UnitConstant(
    'elementary_charge',
    _cd('elementary charge'),
    symbol='e'
)
elementary_charge_over_h = UnitConstant(
    'elementary_charge_over_h',
    _cd('elementary charge over h'),

)
electron_charge_to_mass_quotient = UnitConstant(
    'electron_charge_to_mass_quotient',
    _cd('electron charge to mass quotient'),
    symbol='(-e/m_e)',
    u_symbol='(-e/mₑ)'
)
g_e = electron_g_factor = UnitConstant(
    'electron_g_factor',
    _cd('electron g factor'),
    symbol='g_e',
    u_symbol='gₑ'
)
gamma_e = electron_gyromagnetic_ratio = UnitConstant(
    'electron_gyromagnetic_ratio',
    _cd('electron gyromagnetic ratio'),
    symbol='gamma_e',
    u_symbol='γₑ'
)
electron_gyromagnetic_ratio_over_2_pi = UnitConstant(
    'electron_gyromagnetic_ratio_over_2_pi',
    _cd('electron gyromagnetic ratio over 2 pi'),
    symbol='gamma_e/(2*pi)',
    u_symbol='γₑ/(2·π)'
)
mu_e = electron_magnetic_moment = UnitConstant(
    'electron_magnetic_moment',
    _cd('electron magnetic moment'),
    symbol='mu_e',
    u_symbol='μₑ'
)
a_e = electron_magnetic_moment_anomaly = UnitConstant(

u_symbol='(e²·a₀²/E_h)'
)
atomic_unit_of_electric_potential = UnitConstant(
    'atomic_unit_of_electric_potential',
    _cd('atomic unit of electric potential'),
    symbol='(E_h/e)'
)
atomic_unit_of_electric_quadrupole_moment = UnitConstant(
    'atomic_unit_of_electric_quadrupole_moment',
    _cd('atomic unit of electric quadrupole moment'),
    symbol='(e*a_0**2)',
    u_symbol='(e·a₀²)'
)
atomic_unit_of_energy = UnitConstant(
    'atomic_unit_of_energy',
    _cd('atomic unit of energy'),
)
atomic_unit_of_force = UnitConstant(
    'atomic_unit_of_force',
    _cd('atomic unit of force'),
    symbol='(E_h/a_0)',
    u_symbol='(E_h/a₀)'
)
a_0 = atomic_unit_of_length = UnitConstant(
    'atomic_unit_of_length',
    _cd('atomic unit of length'),
    symbol='a_0',
    u_symbol='a₀'
)
atomic_unit_of_magnetic_dipole_moment = UnitConstant(
    'atomic_unit_of_magnetic_dipole_moment',
    _cd('atomic unit of magnetic dipole moment'),

)
natural_unit_of_action = UnitConstant(
    'natural_unit_of_action',
    _cd('natural unit of action'),
    symbol='hbar',
    u_symbol='ħ'
)
natural_unit_of_energy = UnitConstant(
    'natural_unit_of_energy',
    _cd('natural unit of energy'),
    symbol='(m_e*c**2)',
    u_symbol='(mₑ·c²)'
)
natural_unit_of_length = UnitConstant(
    'natural_unit_of_length',
    _cd('natural unit of length'),
    symbol='lambdabar_C',
    u_symbol='ƛ_C'
)
natural_unit_of_mass = UnitConstant(
    'natural_unit_of_mass',
    _cd('natural unit of mass'),
    symbol='m_e',
    u_symbol='mₑ'
)
natural_unit_of_momentum = UnitConstant(
    'natural_unit_of_momentum',
    _cd('natural unit of momentum'),
    symbol='(m_e*c)',
    u_symbol='(mₑ·c)'
)
natural_unit_of_time = UnitConstant(

symbol='m_e',
    u_symbol='mₑ'
)
eV = electron_volt = UnitConstant(
    'electron_volt',
    _cd('electron volt'),
    symbol='eV'
)
e = elementary_charge = UnitConstant(
    'elementary_charge',
    _cd('elementary charge'),
    symbol='e'
)
elementary_charge_over_h = UnitConstant(
    'elementary_charge_over_h',
    _cd('elementary charge over h'),
    symbol='e/h'
)
F = Faraday_constant = UnitConstant(
    'Faraday_constant',
    _cd('Faraday constant'),
    symbol='F'
)
#F_star = Faraday_constant_for_conventional_electric_current = UnitConstant(
#    _cd('Faraday constant for conventional electric current') what is a unit of C_90?
Fermi_coupling_constant = UnitConstant(
    'Fermi_coupling_constant',
    _cd('Fermi coupling constant'),
    symbol='(G_F/(hbar*c)**3)',
    u_symbol='(G_F/(ħ·c)³)'
)
alpha = fine_structure_constant = UnitConstant(

symbol='(h/(2*pi))',
    u_symbol='ħ'
)
l_P = Planck_length = UnitConstant(
    'Planck_length',
    _cd('Planck length'),
    symbol='l_P'
)
m_P = Planck_mass = UnitConstant(
    'Planck_mass',
    _cd('Planck mass'),
    symbol='m_P'
)
T_P = Planck_temperature = UnitConstant(
    'Planck_temperature',
    _cd('Planck temperature'),
    symbol='T_P'
)
t_P = Planck_time = UnitConstant(
    'Planck_time',
    _cd('Planck time'),
    symbol='t_P'
)
proton_charge_to_mass_quotient = UnitConstant(
    'proton_charge_to_mass_quotient',
    _cd('proton charge to mass quotient'),
    symbol='(e/m_p)'
)
g_p = proton_g_factor = UnitConstant(
    'proton_g_factor',
    _cd('proton g factor'),
    symbol='g_p'