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.. _custom-table:
*************
Custom tables
*************
You can create your own private instance of PeriodicTable and
populate it with values.
Example:
.. doctest::
>>> import periodictable
>>> from periodictable import core, mass, density, elements, formula
>>> mytable = core.PeriodicTable(table="H=1")
>>> mass.init(mytable)
>>> density.init(mytable)
>>> # Reset mass to H=1 rather than C=12
>>> scale = elements.H[1].mass
>>> for el in mytable:
... el._mass /= scale
... if hasattr(el,'_density') and el._density is not None:
... el._density /= scale
... for iso in el:
... iso._mass /= scale
>>> print("%.10f %.10f"%(mytable.H[1].mass, mytable.C[12].mass))
1.0000000000 11.9068286857
>>> print("%.10f %.10f"%(periodictable.H[1].mass, periodictable.C[12].mass))
1.0078250319 12.0000000000
>>> print("%.10f"%formula('2H[1]', table=mytable).mass)
2.0000000000
You will need to add individual properties by hand for all additional
desired properties using ``module.init(elements)``.
The table name (*H=1* above) must be unique within the session. If you
are pickling elements from a custom table, you must create a custom
table of the same name before attempting to restore them. The default
table is just a custom table with the name *public*.
.. Note: If you are using chemical formulas, you will need to
define your own parser using::
from periodictable.formulas import formula_grammar
parser = formula_grammar(table=elements)
Support for custom tables could be made much smoother by delegating
all properties not defined in the custom table back to the base table,
much like is currently done for :class:`Isotopes <periodictable.core.Isotope>`
and :class:`Ions <periodictable.core.Ion>`. That way you only
need to replace the properties of interest rather than defining all
new properties.
The alternative to using custom tables is to replace a dataset in the
base table using e.g., ``custom_mass.init(elements, reload = True)``, where
custom_mass is your own version of the periodic table values. Be aware,
however, that this will have a global effect, changing the mass used by
all packages, so you are strongly discouraged from doing so.
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