comparator 0.2.0

Utility for comparing results between data sources

Comparator

Comparator is a utility for comparing the results of queries run against two databases. Future development will include support for APIs, static files, and more.

Installation

pip install comparator

Usage

Overview

from comparator import Comparator
from comparator.config import DbConfig
from comparator.db import PostgresDb

conf = DbConfig()

l = PostgresDb(**conf.default)
r = PostgresDb(**conf.other_db)
query = 'SELECT * FROM my_table ORDER BY 1'

c = Comparator(l, r, query)
c.run_comparisons()

[('first_eq_comp', True)]

Included Comparisons

There are some basic comparisons included, and they can be imported and passed using constants.

from comparator.comps import BASIC_COMP, LEN_COMP

c = Comparator(l, r, query, comparisons=[BASIC_COMP, LEN_COMP])
c.run_comparisons()

[('basic_comp', True), ('len_comp', True)]

Queries and Exceptions

It's possible to run different queries against each database. You can raise exceptions if that's your speed.

lq = 'SELECT * FROM my_table ORDER BY 1'
rq = 'SELECT id, uuid, name FROM reporting.my_table ORDER BY 1'
comparisons = [BASIC_COMP, LEN_COMP]

c = Comparator(l, r, left_query=lq, right_query=rq, comparisons=comparisons)

for name, success in c.compare():
    if not success:
        raise Exception('{} check failed!'.format(name))

Custom Comparisons

Finally, you'll probably want to define your own comparison checks. You can do so by defining functions that accept left and right args, which, if coming from one of the included database classes, will be a list of tuples representing your query result. Perform whatever magic you like, and return a boolean.

def left_is_longer(left, right):
    # Return True if left contains more rows than right
    return len(left) > len(right)


def totals_are_equal(left, right):
    # Return True if sum(left) == sum(right)
    sl = sr = 0
    for row in left:
        sl += int(row[1])
    for row in right:
        sr += int(row[1])
    return sl == sr


c = Comparator(l, r, query, comparisons=[left_is_longer, totals_are_equal])
c.run_comparisons()

[('left_is_longer', False), ('totals_are_equal', True)]

Changelog

0.1.1 (2018-09-18)

• add query_df methods for returning pandas DataFrames
• add output kwarg to Comparator to allow calling the query_df method

0.1.0 (2018-09-12)

• initial release