Tables in a plug-in

A flowchart’s tables – made by the Table step, or by a step storing its results into a table – are kept in the job’s database, seamm.db, beside the structures (since seamm 2026.10.3; before that they were pandas DataFrames in memory). A table is a flowchart variable whose value is a seamm.Table, a handle on the data in the database.

Writing results

Most plug-ins never touch a table directly: Node.store_results() writes the results the user asked for into the tables they named, creating the table and its columns as needed. The column’s type and default come from the result’s metadata (boolean, integer, float, string; non-scalar results are json). The value goes into the table’s current row; if the current row is past the end of the table, the write appends a row, whose other columns get their defaults.

Working with a table

self.get_table(name) returns the table, creating it if needed (create=False raises instead). Its methods:

columns, n_rows, index_column, column_type(column)

The column names in order, the number of rows, the column identifying rows (or None), and a column’s declared type.

add_column(name, type, default)

Adds a column, filling existing rows with the default; does nothing if the column exists.

append_row(**values), append_rows([dict, ...])

Append rows; missing columns get their defaults; the last row appended becomes the current row.

current_row, locate(key=...), locate(position=...), next_row()

The current row, a row by its index-column value or 0-based position, and moving to the next row (past the last row, the next write appends one).

set_cell(column, value, row=None), get_cell(column, row=None), get_row(row=None)

Values in a row, by default the current one.

rows(where=None)

Iterate over (row, values); where is (column, operator, value[, value2]) with the Loop step’s operators (==, >, between, contains, is empty, …).

to_dataframe(), export(filename), Table.read(...)

A pandas copy for printing, plotting or analysis (changes to it are not saved), writing csv/json/xlsx/txt, and reading a file into a new table.

Rows are identified internally; flowcharts see a row as its index-column value, or its position when the table has no index column.

Code written for the in-memory tables

The handle still answers the old dictionary keys. table["table"] returns a copy of the table as a DataFrame and logs a warning: changes to it are not saved. Assigning a DataFrame to table["table"] replaces the table’s contents. "current index", "index column", "defaults", "filename" and "loop index" work as before. A plug-in that creates its own {"type": "pandas", ...} table cannot work with this seamm; the Table, Loop, Properties and Geometry Analysis steps were converted, and seamm refuses, before the flowchart runs, older versions of them.

Committing

The job database is committed after each step (seamm.step_completed(), called by the flowchart evaluator and the Loop step). A database opened read-only can be read, but writing a table raises PermissionError.