Python Alembic - create column that is pipe delimited concatenation of items in list in json

Question

I'm using alembic to create a new column in a mysql table. The table has a column source_list that is json

{"sources": ["source1" "source2"]}

I want to create a new column, sources, that is a pipe-delimited concatenation of the list items.

"source1|source2"

There is a variable number of sources in the sources list.

The alembic upgrade call would be something like this.

def upgrade():
    op.add_column(
        "table_name",
        sa.Column(
            "sources",
            sa.String(32, collation="utf8mb4_unicode_ci"),
            server_default=sa.Computed("source_list->>'$.sources[0]'"),
        ),
    )

This would create a sources column with the 0th element of the source_list json.

How do I get this computed column of a pipe-delimited concatenation of all the elements in that list?