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A lightweight tool for modeling and simulation of Stochastic Petri Nets (SPNs).

ℹ️Tested with Python 3.11

git clone https://github.com/jo-chr/pyspn.git# 1. Clone repositorypip install -r requirements.txt# 2. Install requirementspython3 examples/one_server.py# 3. Run single-server queue example

Formally, the class of SPNs that can be modeled usingPySPN is defined as:

$$SPN = (P, T, A, G, m_0)$$

where:

• $P = {P_1,P_2,..,P_m}$ is the set of places, drawn as circles;
• $T = {T_1,T_2,..,T_n}$ is the set of transitions along with their distribution functions or weights, drawn as bars;
• $A = A^I \cup A^O \cup A^H$ is the set of arcs, where$A^O$ is the set of output arcs,$A^I$ is the set of input arcs and$A^H$ is the set of inhibitor arcs and each of the arcs has a multiplicity assigned to it;
• $G = {g_1,g_2,..,g_r}$ is the set of guard functions which are associated with different transitions;
• and$m_0$ is the initial marking, defining the distribution of tokens in the places.

Each transition is represented as$T_i = (type, F)$, where$type \in {timed,immediate}$ indicates the type of the transition, and$F$ is either a probability distribution function if the corresponding transition is timed, or a firing weight or probability if it is immediate.

Find sample SPNs underexamples/. Currently, places, timed transitions (t_type = "T"), immediate transitions (t_type = "I"), output arcs, input arcs, inhibitor arcs, guard functions, and memory policies are supported.

A place with its required arguments is defined like so:

p1 = Place(label="Place 1", n_tokens=0)

A timed transition with its required arguments and a sample distribution function is defined like so:

t1 = Transition(label="Transition 1", t_type="T")t1.set_distribution(distribution="expon", a=0.0, b=1.0/1.0)

An immediate transition with its required arguments and a sample weight is defined like so:

t2 = Transition(label="Transition 2", t_type="I")t2.set_weight(weight=0.8)

For timed transitions, some of the supported distributions are:

More distributions can be easily implemented inRNGFactory.py. SeeScipy's documentation for details regarding the distributions and their parameters.

Guard functions are defined like so:

defguard_t1():if len(p1.n_tokens)>= 2:return True    else:return Falset1.set_guard_function(guard_t1)

The default setting is Race Enable ("ENABLE").

The memory policy can be set during instantiation

t1 = Transition(label="Transition_1",t_type="T",memory_policy="AGE")

or by using a function call

t1.set_memory_policy("AGE")

To configure a transition that joins two or more input places, set the "Join" parameter to True.This indicates that the transition will act upon the confluence of tokens from multiple places.

t1 = Transition(label="", t_type="", Join=True)

Similarly, to set up a transition that splits its output to multiple places, utilize the "Fork" parameter.Setting split to True designates that the transition's output will be distributed to several output places.

t1 = Transition(label="", t_type="", Fork=True)

Export and import SPNs aspickle files using theexport_spn() andimport_spn() functions ofspn_io module.

Simulate a SPN like so:

simulate(spn, max_time = 100, verbosity = 2, protocol = True)

For the verbosity there are 3 levels of what is printed in the terminal:

• 0: No information;
• 1: Only final simulation statistics;
• 2: Initial markings, firing of transitions, and final statistics;
• 3: Initial markings, firing of transitions and the resulting marking and state, and final statistics.

The simulation protocol capturing the markings throughtout the simulation can be found underoutput/protocol/.

Visualize a SPN like so:

draw_spn(spn, show=False, file="sample_spn", rankdir="LR")

The graph can be found underoutput/graphs/.

Output graph example for the example "two_server_with_guard&multiplicity.py"

If you are using the tool for a scientific project please consider citing our publications:

# SAGE Publications Sage 2025 (Journal Paper)@article{friederich2025pyspn,  title={PySPN: a Python library for stochastic Petri net modeling, simulation, and event log generation},  author={Friederich, Jonas and Khodadadi, Atieh and Lazarova-Molnar, Sanja},  journal={SIMULATION},  pages={00375497251343625},  year={2025},  publisher={SAGE Publications Sage UK: London, England}}# EAI SIMUtools 2023 - 15th EAI International Conference on Simulation Tools and Techniques (preprint, accepted for presentation)@misc{friederich_2023,    doi = {10.13140/RG.2.2.25334.16967},    url = {https://www.researchgate.net/publication/375758652_PySPN_An_Extendable_Python_Library_for_Modeling_Simulation_of_Stochastic_Petri_Nets},    year = 2023,    month = {Nov},    author = {Friederich, Jonas and Lazarova-Molnar, Sanja},    title = {{PySPN}: An Extendable Python Library for Modeling & Simulation of Stochastic Petri Nets},    conference = {EAI SIMUtools 2023 - 15th EAI International Conference on Simulation Tools and Techniques},    note = {preprint}}

For questions/feedback feel free to contact me:jofr@mmmi.sdu.dk.