Welcome to python-statemachine Discussions!

[fgmacedo]

👋 Welcome!

We’re using Discussions as a place to connect with other members of our community. We hope that you:

• Ask questions you’re wondering about.
• Share ideas.
• Engage with other community members.
• Welcome others and are open-minded. Remember that this is a community we
  build together 💪.

To get started, comment below with an introduction of yourself and tell us about what you do with this community.

[Prasadmarkandey]

hi everyone
i am prasad markandey
i am new beginner for python
can you all please give me a tips how to be a good programmer

[fgmacedo]

Hi @Prasadmarkandey, nice to meet you!

Please let me know: How did you come to know about this library?

Nice that you're learning Python. Do you currently know any other programming language or it's your first approach to programming?

It's hard to say something in a generic way. My way was thought a lot of practice, trying to build things and learning by doing.

[aashishexplorer]

Hello to Python Community!

I have started this traffic light program on my Pycharm and I have installed python-statemachine module also. Configuring all the required things, Pycharm is still dragging me to the same error saying,
ImportError: cannot import name 'Statemachine' from 'statemachine' .
i am on Python 3.8.6
later on changing the import command by just "from statemachine import *" , Pycharm is throwing error saying Statemachine not defined.
Are those classes not available or with some other name, Please help!

[fgmacedo]

Hi Aashish, welcome!

How do you installed the lib? Can you please share the output of the command when you run on the terminal:

pip freeze

[aashishexplorer]

Hello fgmacedo,

I have installed the library following this command, pip install python-statemachine .
is this correct -----> from statemachine import Statemachine, State
because the name of the module is python-statemachine ,while importing we are typing (from statemachine) only.
Is the conflict arrising because of the another library present in python world called statemachine only, whose author is kyle conroy with version 0.1 .
But i have not installed this statemachine library in my site-packages.
I think this is the reason of the issue.

[fgmacedo]

Thanks Aashish. Looks like you have a Python in a virtual env running as your Python Interpreter on Pycharn. And you have installed the statemachine lib globally. Can you verify this? Maybe inside Pycharn you can see a list of available libraries for the current interpreter. Em qua., 31 de mar. de 2021 03:58, Aashish ***@***.***> escreveu:

…

[image: issue1] <https://user-images.githubusercontent.com/67144641/113103074-74b9b800-921c-11eb-8f05-81e346861524.png> Hello fgmacedo, I have installed the library following this command, *pip install python-statemachine* . — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#275 (reply in thread)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AACETLYXC5OWPANC3EADEZ3TGLB27ANCNFSM4ZDDXQZQ> .

[fgmacedo]

This is intriguing...

My thought is that you may have another file/module called statemachine
in your importing paths that is taking precedence over the installed lib.

Can you please share the output of these commands?

import sys
import statemachine

statemachine_modules = [(name, module.__file__) for name, module in sys.modules.items() if 'statemachine' in name]

print(f"dir: {dir(statemachine)}\r\n")
print(f"__file__: {statemachine.__file__}\r\n")
print(f"modules: {statemachine_modules}")

[aashishexplorer]

hello fgmacedo,

The output of the above mentioned commands is:

F:\Python_Projects\StateMachine\venv\Scripts\python.exe F:/Python_Projects/StateMachine/source/StateMachineCode.py
dir: ['State', 'StateMachine', 'Transition', 'all', 'author', 'builtins', 'cached', 'doc', 'email', 'file', 'loader', 'name', 'package', 'path', 'spec', 'version', 'absolute_import', 'exceptions', 'registry', 'statemachine', 'unicode_literals', 'utils']

file: F:\Python_Projects\StateMachine\venv\lib\site-packages\statemachine_init_.py

modules: [('statemachine.registry', 'F:\Python_Projects\StateMachine\venv\lib\site-packages\statemachine\registry.py'), ('statemachine.utils', 'F:\Python_Projects\StateMachine\venv\lib\site-packages\statemachine\utils.py'), ('statemachine.exceptions', 'F:\Python_Projects\StateMachine\venv\lib\site-packages\statemachine\exceptions.py'), ('statemachine.statemachine', 'F:\Python_Projects\StateMachine\venv\lib\site-packages\statemachine\statemachine.py'), ('statemachine', 'F:\Python_Projects\StateMachine\venv\lib\site-packages\statemachine\init.py')]

Process finished with exit code 0

[fgmacedo]

Oh, it's everything ok, now I see that is happening. Reviewed your error message and It's only a case mismatch. Python is a case sensitive language, so Statemachine is not equal to StateMachine.

Change your import line to:

from statemachine import StateMachine

[aashishexplorer]

Oh!
i am very sorry for being so silly while reading the example. This typing of all the code through fingers has made me do this silly mistake.
i would have never ended in this trap if i had reused the code. sorry, for wasting your time.
Thank you so much for your time and efforts. <3

[fgmacedo]

Hey, no problem. It happens.

Looking forward to see that you'll build next.

Best regards!

[bp100a]

I am using your statemachine class in a Python project. I'm trying to use inheritance. So I would do the following:

class BasicSM(StateMachine):

class FancierSM(BasicSM):

class FanciestSM(BasicSM):

The issue I'm having is that the transitions & states appear to "co-mingle" as class variables, so all transitions & states are present in all instances. So the actual state (self.current_state) is an instance variable, but the state definitions are all class variables.

So how would allow for inheritance that is not visible to "sibling" classes?

[fgmacedo]

Hi Harry, nice to meet you. Thanks for getting in touch.

Can you please provide a concrete example of those classes and what exactly is the unexpected behaviour? Something similar to an automated test that is failing so I can figure out the problem and a possible solution?

Something like this:

class CampaignMachine(StateMachine):
    "A workflow machine"
    draft = State('Draft', initial=True)
    producing = State('Being produced')
    closed = State('Closed')  # Should raise an Exception when instantiated

    add_job = draft.to(draft) | producing.to(producing)
    produce = draft.to(producing)
    deliver = producing.to(closed)


machine = CampaignMachine()

assert machine.current_state is CampaignMachine.draft  # this is expected to be true

And if you feel comfortable, consider adding an automated test that reproduces the issue, we've a few scenarios covered for inheritance here: https://github.com/fgmacedo/python-statemachine/blob/develop/tests/test_statemachine_inheritance.py

[the-cmk]

I am trying to migrate a program written with a PLC (programmable logic controller) to Python using your library. There are a few things I am confused about how to implement here. First is with transitions, I would like one transition "state_completed" to complete the transition from one state to another depending on what state we are in. For example --> if I am in the "Starting" state, then "state_completed" should allow me transition to "Running" state. Similarly, if I am in "Stopping" state, then, state completed should allow me to move to "Stopped" state. In essence, this could be implemented like, "state_completed = State("whatever") if current_state == test_state".

2nd question and most important is on the callbacks. I would like to wait on the callbacks without blocking my program. For example:
def on_enter_starting(self):
start microwave()
wait until microwave finish sequence

but not blocking the rest of my program. I have tried asyncio, but I cannot get the current_event_loop since there is no constructor. Please advise.

[brunolnetto]

Hi, @the-cmk

We are glad to have you with us and consider python-statemachine a great library. We recommend you to introspect a bit about state machine concept:

1. It is not a good practice to use action verbs as states because of linguistics: states are inertial-descriptive words, while transitions are action-driven. Therefore, consider changing nomenclature to "idle", "functional" "paused" "shut off";

2. This state machine as a library is well-suited to describe. It means, these application-related details are up to those apply to resolve. Your description seems close to a javascript async-await description, which waits by default the execution. The library asyncio seems great, and promising (no pun intended) eith python-statemachine.

[ataberken]

Hello,

How can I execute a piece of code after transitioned to a State?

For instance for the below code, when the state is 'Green', I would like to print('Green') and execute 'slowdown' to change the state from 'Green' to 'Yellow' automatically. (My Objective is a bit more complex than this, but if you can help me to understand this one, I can figure out the rest)

from statemachine import StateMachine, State

class TrafficLightMachine(StateMachine):
    green = State('Green', initial=True)
    yellow = State('Yellow')
    red = State('Red')

    slowdown = green.to(yellow)
    stop = yellow.to(red)
    go = red.to(green)

traffic_light = TrafficLightMachine()

Would be happy if you can support me when available..

[danielkanzel]

def on_enter_green(self):
    print('Green')
    self. slowdown()

[fgmacedo]

Closing as this thread is stale for a while.