store/access activity metadata in datapackage created with brightway data - brightway

Question

When I define a datapackage with with bw2data. How can I access metadata associated with the activities ? lets say I create a simple database :
# biosphere
bio_db = bd.Database("mini_biosphere")
bio_db.register()
co2 = bio_db.new_activity(code = 'CO2',
name = 'carbon dioxide',
categories=('air',),
type='emission',
unit='kg')
co2.save()
ch4 = bio_db.new_activity(code = 'CH4',
name = 'methane',
categories=('air',),
type='emission',
unit='kg')
ch4.save()
# technosphere
a_key = ("testdb", "a")
b_key = ("testdb", "b")
act_a_def = {
'name': 'a',
'unit': 'kilogram',
'comment':'just saying',
'exchanges': [{"input": co2.key, "type": "biosphere", "amount": 10},
{"input": a_key, "output":a_key,'type':'production','amount':1},
{"input": b_key, "output":a_key,'type':'substitution','amount':1},
],
}
act_b_def = {
'name': 'b',
'unit': 'kilogram',
'comment':'it depends',
'exchanges': [
{"input": b_key, "output":a_key,'type':'production','amount':1},
{"input": ch4.key, "type": "biosphere", "amount": 1},
],
}
db = bd.Database("testdb")
db.write(
{
a_key : act_a_def,
b_key : act_b_def
}
)
I can read the metadata of the associated datapackage with db.datapackage().metadata an even perform a calculation (as done here)... but data such as the name of the activities or the comments seems to be missing. Where is it stored or what needs to be done to store it ?

Answer 1

By default, datapackages don't have metadata of this nature - their whole point is to just have the numeric values for matrix creation. You would normally query the Database object to get such metadata.
However, you can ask for this metadata to be written as well. You will need to process the database again, with (in your example) db.process(csv=True). In this case, you will get an additional resource, <database name>_activity_metadata, which is loaded as a Pandas DataFrame. In the example, this would be retrieved with dp.get_resource('testdb_activity_metadata')[0].
Note that there was a bug, so this functionality requires bw2data version 4.0.dev16 or higher (released 2022-06-09).