Pl python python w postgre-sql

PL/Python - Python in PostgreSQL

Stored procedures
● subroutine available to applications that
access RDBMS
● callable from SQL
● more complicated tasks

Stored procedures - example
create function kariera_it(year int) returns varchar AS
$$
begin
return 'Karieta IT ' || year::varchar;
end
$$ language plpgsql;

Stored procedures - example
pystok=# select kariera_it(2017);
kariera_it
--------------------
Kariera IT 2017
(1 wiersz)

Stored procedures
● many languages
● official support for PL/Perl, PL/Python,
PL/Tcl, PL/pgSQL
● unofficial: Ruby, Java, R, V8, PHP

PL/Python
● untrusted
● available Python 2 and 3
● default Python 2

PL/Python
CREATE EXTENSION plpythonu, or from
the shell command line use createlang
plpythonu dbname

PL/Python
● Python Interpreter is initialised inside backend process
● Postgres types are transformed into Python types
● additional modules and variables are initialised

PL/Python
CREATE FUNCTION funcname (argument-list)
RETURNS return-type
AS $$
# PL/Python function body
$$ LANGUAGE plpythonu;
● BODY -> Python code
● get arg-list, return value
● if not returned - function returns None

PL/Python - say Hello
create function pymax (a integer, b integer)
returns integer
as $$
return a if a>b else b
$$ language plpythonu;

PL/Python
def __plpython_procedure_pymax_23456():
● 23456 - OID

PL/Python
def __plpython_procedure_pymax_23456():
● 23456 - OID
● arguments are set as global variables
● tip of the day: treat function parameters as
read-only

PL/Python
● each function gets its own execution environment in the
Python interpreter
● global data and function arguments from myfunc are
not available to myfunc2
● exception - global dictionary GD

PL/Python - example
create or replace function kariera_it(year integer) returns varchar as
$$
return 'Kariera IT {}'.format(year)
pystok=# select kariera_it(2017);
kariera_it
------------------
Kariera IT 2017
(1 wiersz)

PL/Python - Data Types Mapping
PostgreSQL Python
smallint, int int
bigint, oid long (Python 2), int (Python 3)
real float
numeric Decimal (cdecimal lub decimal)
varchar, other str types str (Python 2 PostgresSQL
encoding, Python 3 Unicode)

PL/Python - Composite Types
create table pystok (
edition_nr integer,
beer_quantity integer,
good_speakers boolean
);
create or replace function is_good_party(edition pystok)
returns boolean
as $$
if edition['beer_quantity'] > 50 and edition['good_speakers']:
return True
return False

PL/Python - Composite Types
pystok=# insert into pystok (edition_nr, beer_quantity,
good_speakers) values (23, 100, True);
pystok=# select is_good_party(pystok) happy from pystok;
happy
-------
t
(1 wiersz)

PL/Python - Triggers
● automatically executed or fired when some events
occur
● e.g. UPDATE on table
● benefits:
○ event logging
○ generating some derived column values
automatically
○ validate data

● When a function is used as a trigger, the dictionary TD contains
trigger-related values
TD[‘event’] INSERT, UPDATE, DELETE,
TRUNCATE
TD[‘when’] BEFORE, AFTER, INSTEAD OF
TD[‘new’], TD[‘old’] new/old values (depending on
triggered event)
and more…

create or replace function check_active()
returns trigger as $$
class UserNotActive(Exception): pass
if not TD["old"]["active"] and not TD["new"]["active"]:
raise UserNotActive

create trigger change_username
before update on profile
for each row execute procedure
check_active();
insert into profile (username, active) values
('Marik1234', False);

pystok=# UPDATE profile SET username='TheMarik1234'
WHERE id=1;
ERROR: UserNotActive:
KONTEKST: Traceback (most recent call last):
PL/Python function "check_active", line 5, in <module>
raise UserNotActive
PL/Python function "check_active"

PL/Python - Python modules
CREATE FUNCTION get_file_ext(file_path varchar)
returns varchar as
$$
import os
filename, file_ext = os.path.splitext(file_path)
return file_ext;

PL/Python - Python modules
pystok=# select get_file_ext('/path/to/my/file/pystok.html');
get_file_ext
--------------
.html
(1 wiersz)

PL/Python - DB Access
create function my_func() returns setof profile
as $$
rv = plpy.execute("SELECT * FROM profile", 5);
for x in rv:
yield x

DO
$$
plan = plpy.prepare("INSERT INTO mytable (myval) values
($1)", ['text'])
plpy.execute(plan, ['my value'])

● when you prepare a plan using the PL/Python module it is automatically
saved
● you can use SD or GD dictionaries
if "plan" in SD:
plan = SD["plan"]
else:
plan = plpy.prepare("SELECT 1")
SD["plan"] = plan

PL/Python - example
create table product(
id serial primary key not null,
product_name varchar(256),
price decimal(7,2),
quantity int,
);
create table sold_out(
product_id int references product (id),
created_at timestamp default now()
);
create table error_log (
error_type varchar(64),
error_msg varchar(512),
raised_at timestamp default now()
)
insert into product (product_name,
price, quantity) values ('Harnas',
1.89, 10);

PL/Python - example
create or replace function check_quantity()
returns trigger
as $$
import smtplib
if TD["new"]["quantity"] == 0:
plan = plpy.prepare("INSERT INTO sold_out (product_id) VALUES ($1)",
['int'])
plpy.execute(plan, [TD["new"]["id"]])
…………………………………………………………………………………………….

PL/Python - example
sender, receiver = ('from@gmail.com', 'to@gmail.com')
msg = "rn".join([
"From: {}".format(sender),
"To: {}".format(receiver),
"Subject: {} sold out!".format(TD["new"]["product_name"]),
"",
"{}: {} sold out".format(TD["new"]["id"],
TD["new"]["product_name"])
])

PL/Python - example
try:
server = smtplib.SMTP('localhost')
server.sendmail(sender, receiver, msg)
except (smtplib.SMTPException, smtplib.SMTPAuthenticationError) as e:
plan = plpy.prepare("INSERT INTO error_log (error_type, error_msg)
values ($1, $2)", ['text', 'text'])
plpy.execute(plan, ('SMPTException', e))

PL/Python - example
create trigger product_update
before update on product
for each row execute procedure
check_quantity();
update product set quantity=0 where id=1;

PL/Python - Subtransactions
CREATE FUNCTION transfer_funds() RETURNS void AS $$
try:
plpy.execute("UPDATE accounts SET balance = balance - 100 WHERE
account_name = 'joe'")
plpy.execute("UPDATE accounts SET balance = balance + 100 WHERE
account_name = 'mary'")
except plpy.SPIError, e:
result = "error transferring funds: %s" % e.args
else:
result = "funds transferred correctly"
plan = plpy.prepare("INSERT INTO operations (result) VALUES ($1)", ["text"])
plpy.execute(plan, [result])

PL/Python - Subtransactions
CREATE FUNCTION transfer_funds2() RETURNS void AS $$
try:
with plpy.subtransaction():
plpy.execute("UPDATE accounts SET balance = balance - 100 WHERE
account_name = 'joe'")
plpy.execute("UPDATE accounts SET balance = balance + 100 WHERE
account_name = 'mary'")
except plpy.SPIError, e:
result = "error transferring funds: %s" % e.args
else:
result = "funds transferred correctly"
plan = plpy.prepare("INSERT INTO operations (result) VALUES ($1)", ["text"])

PL/Python - summary
● Python is a nicer language than PL/pgSQL
● ability to use Python libraries
● can communicate with other services

Now to our team, we are looking for:
1. Senior Software Engineer – x4
2. Senior Python Developer – x4
3. Senior Frontend Developer – x2
4. QA Tester – x1
5. Mobile Developer – x1
6. Data Scientist – x3

Questions?
piotrpalkiewicz@gmail.com

Pl python python w postgre-sql

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