module

dframeio.postgres

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Access PostgreSQL databases using psycopg3.

Classes
class

dframeio.postgres.PostgresBackend(conninfo=None, autocommit=True)

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Bases
dframeio.abstract.AbstractDataFrameReader dframeio.abstract.AbstractDataFrameWriter

Backend to read and write PostgreSQL tables

Parameters
  • conninfo (str, optional) — Connection string in libq format. See the PostgreSQL docs for details.
Raises
  • TypeError — If any of the input arguments has a diffent type as documented
  • ValueError — If any of the input arguments are outside of the documented value ranges or if conflicting arguments are given.
Methods
  • read_to_dict(source, columns, row_filter, limit, sample, drop_duplicates) (dict(str: )) — Read data into a dict of named columns</>
  • read_to_pandas(source, columns, row_filter, limit, sample, drop_duplicates) (DataFrame) — Read a postgres table into a pandas DataFrame</>
  • write_append(target, dataframe) — Write data in append-mode to a Postgres table</>
  • write_replace(target, dataframe) — Write data to a Postgres table after deleting all the existing content</>
method

read_to_pandas(source, columns=None, row_filter=None, limit=-1, sample=-1, drop_duplicates=False)

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Read a postgres table into a pandas DataFrame

Parameters
  • source (str) — The table name (may include a database name)
  • columns (list of str, optional) — List of column names to limit the reading to
  • row_filter (str, optional) — Filter expression for selecting rows
  • limit (int, optional) — Maximum number of rows to return (limit to first n rows)
  • sample (int, optional) — Size of a random sample to return
  • drop_duplicates (bool, optional) — Whether to drop duplicate rows from the final selection
Returns (DataFrame)

A pandas DataFrame with the requested data.

Raises
  • ValueError — If path specified with source is outside of the base path

The logic of the filtering arguments is as documented for read_to_pandas().

method

read_to_dict(source, columns=None, row_filter=None, limit=-1, sample=-1, drop_duplicates=False)

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Read data into a dict of named columns

Parameters
  • source (str) — A string specifying the data source (format differs by backend)
  • columns (list of str, optional) — List of column names to limit the reading to
  • row_filter (str, optional) — NOT IMPLEMENTED. Reserved keyword for filtering rows.
  • limit (int, optional) — Maximum number of rows to return (top-n)
  • sample (int, optional) — Size of a random sample to return
  • drop_duplicates (bool, optional) — Whether to drop duplicate rows
Returns (dict(str: ))

A dictionary with column names as key and a list with column values as values

The logic of the filtering arguments is as documented for read_to_pandas().

method

write_replace(target, dataframe)

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Write data to a Postgres table after deleting all the existing content

Parameters
  • target (str) — The database table to write to.
  • dataframe (Union(dataframe, dict(str: ))) — The data to write as pandas.DataFrame or as a Python dictionary in the format column_name: [column_data]
Raises
  • TypeError — When the dataframe is neither a pandas.DataFrame nor a dictionary
method

write_append(target, dataframe)

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Write data in append-mode to a Postgres table

Parameters
  • target (str) — The database table to write to.
  • dataframe (Union(dataframe, dict(str: ))) — The data to write as pandas.DataFrame or as a Python dictionary in the format column_name: [column_data]
Raises
  • TypeError — When the dataframe is neither a pandas.DataFrame nor a dictionary