SAGAS
A simple async sagas implementation
Installation
$ pip install pysagas
Usage
Simple example
import asyncio
from sagas import SagaBuilder
counter = [10, 20]
amount = 30
def add(amount, index):
"""Increments array index by amount
Args:
amount (int): increment value
index (int): index of value to increment
"""
counter[index] += amount
def decrement(amount, index):
"""Decrements array index by amount
Args:
amount (int): decrement value
index (int): index of value to decrement
"""
counter[index] -= amount
return counter
saga_builder = SagaBuilder.create()
saga = saga_builder\
.add_step(lambda: add(amount, 0), lambda: decrement(amount, 0))\
.add_step(lambda: add(amount, 1), lambda: decrement(amount, 1))\
.build()
if __name__ == "__main__":
asyncio.run(saga.run(exceptions=(OSError)))
print(counter) # [40, 50]Failure example
If one step fails, the compensating functions for the executed steps run and the counter values are compensated
import asyncio
from sagas import SagaBuilder
counter = [10, 20]
amount = 30
def add(amount, index):
"""Increments array index by amount
Args:
amount (int): increment value
index (int): index of value to increment
"""
counter[index] += amount
raise Exception('error occurred')
def decrement(amount, index):
"""Decrements array index by amount
Args:
amount (int): decrement value
index (int): index of value to decrement
"""
counter[index] -= amount
return counter
saga_builder = SagaBuilder.create()
saga = saga_builder\
.add_step(lambda: add(amount, 0), lambda: decrement(amount, 0))\
.add_step(lambda: add(amount, 1), lambda: decrement(amount, 1))\
.build()
if __name__ == "__main__":
asyncio.run(saga.run(exceptions=(OSError, Exception)))
print(counter) # [10, 20]
