Pint-Pandas in your projects

Pint-Pandas in your projects#

Using a Shared Unit Registry#

As described in the documentation of the main pint package::

If you use Pint in multiple modules within your Python package, you normally want to avoid creating multiple instances of the unit registry. The best way to do this is by instantiating the registry in a single place. For example, you can add the following code to your package __init__.py

When using pint_pandas, this extends to using the same unit registry that was created by the main pint package. This is done by using the pint.get_application_registry() function.

In a sample project structure of this kind:

.
└── mypackage/
    ├── __init__.py
    ├── main.py
    └── mysubmodule/
        ├── __init__.py
        └── calculations.py

After defining the registry in the mypackage.__init__ module:

from pint import UnitRegistry, set_application_registry
ureg = UnitRegistry()
ureg.formatter.default_format = "P"

set_application_registry(ureg)

In the mypackage.mysubmodule.calculations module, you should get the shared registry like so:

import pint
ureg = pint.get_application_registry()

@ureg.check(
    '[length]',
)
def multiply_value(distance):
    return distance * 2

Failure to use the application registry will result in a DimensionalityError of the kind:

Cannot convert from ‘<VALUE> <UNIT>’ ([<DIMENSION>]) to ‘a quantity of’ ([<DIMENSION>])”.

For example:

DimensionalityError: Cannot convert from '200 metric_ton' ([mass]) to 'a quantity of' ([mass])"
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