Description:
saga py 1.1.0
Create a series of dependent actions and roll everything back when one of them fails.
Install
$ pip install saga_py
Usage
Simple example
from saga import SagaBuilder
counter1 = 0
counter2 = 0
def incr_counter1(amount):
global counter1
counter1 += amount
def incr_counter2(amount):
global counter2
counter2 += amount
def decr_counter1(amount):
global counter1
counter1 -= amount
def decr_counter2(amount):
global counter2
counter2 -= amount
SagaBuilder \
.create() \
.action(lambda: incr_counter1(15), lambda: decr_counter1(15)) \
.action(lambda: incr_counter2(1), lambda: decr_counter2(1)) \
.action() \
.build() \
.execute()
# if every action succeeds, the effects of all actions are applied
print(counter1) # 15
print(counter2) # 1
An action fails example
If one action fails, the compensations for all already executed actions are run and a SagaError is raised that wraps
all Exceptions encountered during the run.
from saga import SagaBuilder, SagaError
counter1 = 0
counter2 = 0
def incr_counter1(amount):
global counter1
counter1 += amount
def incr_counter2(amount):
global counter2
counter2 += amount
raise BaseException('some error happened')
def decr_counter1(amount):
global counter1
counter1 -= amount
def decr_counter2(amount):
global counter2
counter2 -= amount
try:
SagaBuilder \
.create() \
.action(lambda: incr_counter1(15), lambda: decr_counter1(15)) \
.action(lambda: incr_counter2(1), lambda: decr_counter2(1)) \
.action() \
.build() \
.execute()
except SagaError as e:
print(e) # wraps the BaseException('some error happened')
print(counter1) # 0
print(counter2) # 0
An action and a compensation fail example
Since the compensation for action2 fails, the compensation effect is undefined from the framework’s perspective,
all other compensations are run regardless.
from saga import SagaBuilder, SagaError
counter1 = 0
counter2 = 0
def incr_counter1(amount):
global counter1
counter1 += amount
def incr_counter2(amount):
global counter2
counter2 += amount
raise BaseException('some error happened')
def decr_counter1(amount):
global counter1
counter1 -= amount
def decr_counter2(amount):
global counter2
raise BaseException('compensation also fails')
try:
SagaBuilder \
.create() \
.action(lambda: incr_counter1(15), lambda: decr_counter1(15)) \
.action(lambda: incr_counter2(1), lambda: decr_counter2(1)) \
.action() \
.build() \
.execute()
except SagaError as e:
print(e) #
print(counter1) # 0
print(counter2) # 1
Passing values from one action to the next
An action can return a dict of return values.
The dict is then passed as keyword arguments to the next action and it’s corresponding compensation.
No values can be passed between compensations.
from saga import SagaBuilder, SagaError
counter1 = 0
counter2 = 0
def incr_counter1(amount):
global counter1
counter1 += amount
return {'counter1_value': counter1}
def incr_counter2(counter1_value):
global counter2
counter2 += amount
def decr_counter1(amount):
global counter1
counter1 -= amount
def decr_counter2(counter1_value):
global counter2
counter2 -= amount
SagaBuilder \
.create() \
.action(lambda: incr_counter1(15), lambda: decr_counter1(15)) \
.action(incr_counter2, decr_counter2) \
.action() \
.build() \
.execute()
print(counter1) # 15
print(counter2) # 15
License
For personal and professional use. You cannot resell or redistribute these repositories in their original state.
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