sfconn 0.3.3

Snowflake connection helper functions

sfconn

Snowflake connection helper functions

A Python library to simplify connecting to Snowflake databases

Notes

1. This is a major version upgrade and breaks compatibility with the previous versions (< 0.3.0). sfconn now relies on snowflake-python-connector for accessing named connections (connections.toml).
2. sfconn optionally modifies the way private_key_file connection option is evaluated. When --keyfile-pfx-map option is specified, or if $SFCONN_KEYFILE_PFX_MAP is set, (option value must be a pair of source and target paths separated by :). private_key_file option, if present and begins with the source path, it is temporarily modified as if it begins with the target path. Primary use-case is to be able to maintain one copy of connections.toml file across different execution environments, such as within containers.

Installation

Use Python's standard pip utility for installation:

pip install --upgrade sfconn

Usage

getconn() and getsess()

getconn and getsess are wrapper functions over native Snowflake functions with added functionality (mainly mapping private_key_file value as described above).

Note: getsess() function will be available only if snowflake-snowpark-python package is available at run-time.

Usage:

def getconn(connection_name: str | None, **overrides: dict[str, Any]) -> Connection:
def getsess(connection_name: str | None, **overrides: dict[str, Any]) -> Session:

getconn and getsess accept a connection name and return a connection or session object respectively with modified behavior as noted above.

Examples:

from sfconn import getconn

# assuming 'dev' is a named connection defined in connections.toml
with getconn('dev', schema='PUBLIC') as cnx:
    with cnx.cursor() as csr:
        csr.execute('SELECT CURRENT_USER()')
        print("Hello " + csr.fetchone()[0])

from sfconn import getsess

# assuming 'dev' is a named connection defined in connections.toml
with getsess('dev', schema='PUBLIC') as session:
    df = sess.sql("select current_user() as curr_user, current_role() as curr_role")
    print(df.collect())

run_query*()

Cursor objects add a family of few convenience methods that return an Iterable of values instead of generic tuple or dict.

1. <cursor>.run_query(<callable>|<class>, <sql> [,<params>]): Returns an Iterable of values.
   • <callable> is a mapping function that shall accept all column values of a row as individual arguments, in order, and returns a value that will be used for Iterable.
   • <class> is any Python class whose attribute names, after upper-casing, are treated as column names from the result set. <class> can include only a subset of a all available column from the query result as attributes and in a different order than the query.
2. <cursor>.run_query1(<callable>|<class>, <sql> [,<params>]): Similar to run_query, except returns a single value. Note, if at least one value is not available, raises ProgrammingError exception.
3. <cursor>.run_query1_opt(<callable>|<class>, <sql> [,<params>]): Similar to run_query1, except instead of raising an exception, the method returns None.

Examples:

import datetime as dt
from collections import namedtuple

Result = namedtuple("Result", ["user", "date"])

def mkResult(x: str, y: dt.date) -> Result:
    return Result(x, y)

with getconn() as cnx, cnx.cursor() as csr:
    result = csr.run_query1(mkResult, "select current_user() as user, current_date() as date")

import datetime as dt
from dataclasses import dataclass

@dataclass
class Result:
    date: dt.date
    user: str

with getconn() as cnx, cnx.cursor() as csr:
    result = csr.run_query1(
        Result,
        "select current_user() as user, current_date() as date, current_warehouse() as wh_name"
    )

Decorator Functions

Python command-line scripts that use argparse library, can use decorator functions to further reduce boilerplate code needed for setting up a Snowflake connection and error checking

def with_connection_args(doc: str | None) -> Callable[[argparse.ArgumentParser], None]:
def with_connection(logger = None) -> Callable[[Connection, ...], None]:
def with_session(logger = None) -> Callable[[Session, ...], None]:

with_connection_args() decorator function:

1. builds an ArgumentParser object
2. adds common Snowflake connection options as arguments including overriding role, database, schema and warehouse
3. calls the decorated function with the parser object to allow adding any script specific options

with_connection() decorator function:

1. consumes standard Snowflake connection options (specified with with_connection_args())
2. creates a connection object
3. calls the decorated function with a connection object as first parameter and any other script specific options that were specified on command line

with_session() decorator function:

1. Similar to with_connection() but creates a snowflake.snowpark.Session object instead of a connection object
2. Note: this decorator will be available only if snowflake-snowpark-python package is available at run-time.

Note: Decorator function parenthesis cannot be omitted even if no arguments are supplied to the decorator functions

Example:

from sfconn import with_connection_args, with_connection

@with_connection()
def main(con, show_account: bool):
    with con.cursor() as csr:
        csr.execute('SELECT CURRENT_USER()')
        print("Hello " + csr.fetchone()[0])
        if show_account:
            csr.execute("SELECT CURRENT_ACCOUNT()")
            print("You are connected to account: " + csr.fetchone()[0])

@with_connection_args("Sample application that greets the current Snowflake user")
def getargs(parser):
    parser.add_argument("-a", "--show-account", action='store_true', help="show snowflake account name")

if __name__ == '__main__':
    main(**vars(getargs()))

get_token()

Function sfconn.get_token() returns a JWT token for connections that use private_key_path option. An optional lifetime value can be specified (default 54 minutes)

Example:

from sfconn import get_token
jwt_token = get_token(None, 120)  # get token using default (None) connection, and valid for 120 minutes