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"""oslo.db enginefacade with intelligent retries demonstration.

This script illustrates three API functions:

* run_api_call_always_outermost - this API call is always outside of any
  transactional context.   A decorator asserts that this is the case.
  Database errors that occur within it will trigger
  the whole function to be retried.

* run_internal_api_call - this API call is always called inside of a

zzzeek

"""pep-409 and pep-415 add support for "raise exception from None" so that
libraries need not expose internal exception cases.

However, this is too broad in scope as it breaks user-land code that would
like to still see the context of where *their* application was handling
the error.

This makes pep-409/415 more or less useless and the problem they'd like
to solve still remains unsolved.

zzzeek

###################################################################
# OLD WAY:

q = session.query(User).options(selectinload(User.addresses))

# result_iter is an iterator
result_iter = iter(q.yield_per(5))


###################################################################

zzzeek

"""
this demonstration illustrates how a library like pandas could
theoretically (or maybe it does already with some flag?) not require
a copy of the data when an operation takes place on the structure.
this is based on the article https://pythonspeed.com/articles/minimizing-copying/
which illustrates specific programming techniques that can be used with a numpy
array in order to minimize data copying; this gist presents an alternative by
which the library could perhaps sheild this implementation detail from the
end-user.
"""

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from sqlalchemy import Column
from sqlalchemy import create_engine
from sqlalchemy import ForeignKey
from sqlalchemy import Integer
from sqlalchemy import String
from sqlalchemy import Table
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship
from sqlalchemy.orm import Session

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test=> create table foo (a integer, b integer, c integer);
CREATE TABLE
test=> insert into foo (a, b, c) values (1, 2, 3);
INSERT 0 1
test=> -- dupe column names are OK
test=> select a as a, b as b, c as c, a as a, b as a, b as b from foo;
 a | b | c | a | a | b 
---+---+---+---+---+---
 1 | 2 | 3 | 1 | 2 | 2
(1 row)

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""" "Writing SQL is just as fast as using an ORM" proof of concept

Below is a simple Python object model, where we represent a database that
stores the names of employees at a company, some of whom are "engineers",
and a list of the jobs they do and the programming languages they use.

We'd like to persist the state represented by this Python object model
in a relational database, using our Python objects as a start.  Then we'd
like to write SQL queries for rows in this database, and we get back instances
of Python objects exactly as they were created.

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import random
import time as blocking_time

import eventlet
import pymysql

# monkeypatch Python network libraries so that they are non blocking. all
# Python code that uses the pure Python network IO functions will be non
# blocking, where all  IO waiting will defer back to eventlet where it will
# pass off work to another greenlet.

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# So interestingly, Signature seems to be twice as fast in Python 3.6 and 3.7 as it 
# was in Python 3.3 and 3.4.  However, it is still 6-18 times slower than the old
# getargspec or getfullargspec that was in Python 3.3.

Python 2.7 getargspec (doesn't use Signature)         : specimen_one (6 args)   : 0.0503
Python 2.7 getargspec (doesn't use Signature)         : specimen_two (0 args)   : 0.0496
Python 2.7 getargspec (doesn't use Signature)         : specimen_three (6 args) : 0.0500
Python 2.7 getargspec (doesn't use Signature)         : specimen_four (13 args) : 0.0652

Python 3.3 getfullargspec (doesn't use Signature)     : specimen_one (6 args)   : 0.0539

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# note: we are using SQLAlchemy that includes _cache_key
# currently at:
# https://gerrit.sqlalchemy.org/#/c/sqlalchemy/sqlalchemy/+/1204/5/

import typing

from sqlalchemy import bindparam
from sqlalchemy import Column
from sqlalchemy import func
from sqlalchemy import inspection