StepSim - Python Step-based Simulation Package
Project description
About
StepSim is a lightweight step-based simulation module written in Python. It can do simple real-time simulations of discrete systems. StepSim supports step-by-step simulation or can run until a break condition occurs.
Simulations are made up of containers and converters. A container stores a discrete amount of units of a certain type. A converter draws units from one or more containers and delivers the result to another container.
StepSim does not even attempt to do any parallel processing. It processes converters round-robin in a fixed order.
Prerequisites
Python (tested on Python 3.1.2 and 2.6.5) http://www.python.org
Installation
Unzip the file, then at the command line run
python setup.py install
Running Tests
Open a shell / DOS window, navigate to the stepsim directory, and run
python -m doctest README
Documentation
To read the API documentation, open a shell / DOS window, navigate to the stepsim directory, and run
pydoc stepsim
You can create a HTML version using
pydoc -w stepsim
Example
First import the stepsim module:
>>> import stepsim
To get verbose output, activate logging to console:
>>> stepsim.log_to_stdout()
>>> stepsim.loglevel("debug")
Now create some containers:
>>> cashbox = stepsim.Container("cashbox", "EUR", 10)
>>> storage = stepsim.Container("storage", "parts")
Then create a converter and set up the draw-deliver-ratio:
>>> buyer = stepsim.Converter("buyer", 2, (cashbox, 3), (storage, 1))
buyer: Adding source 'cashbox', drawing 3 EUR per step.
From any list of converters, we can get a list of simulation milestones that lead to an end condition (without actually running a simulation):
>>> stepsim.loglevel("info")
>>> stepsim.milestones("storage == 3", [buyer])
------------------------------
Milestones to achieve storage == 3:
<BLANKLINE>
Milestone:
9 EUR in cashbox (10 in stock, 111.11%)
total: 100.0%
<BLANKLINE>
Milestone:
3.0 parts in storage (0 in stock, 0.0%)
total: 0.0%
------------------------------
[<Milestone (cashbox: 9) 100.0%>, <Milestone (storage: 3.0) 0.0%>]
Let’s create a simulation:
>>> stepsim.loglevel("debug")
>>> s = stepsim.Simulation(buyer)
Adding converter 'buyer' to simulation.
Current containers: ['cashbox', 'storage']
>>> s
<Simulation consisting of [<buyer: converting from ['cashbox'] to storage>]>
The step() method is used to advance the simulation by one step:
>>> stepsim.loglevel("info")
>>> s.step()
buyer: Drawing 3 EUR from cashbox.
It is also possible to check conditions inbetween. The simulation instance offers a convenience method to do this using a string describing the condition:
>>> s.check("cashbox == 10")
False
>>> s.check("cashbox != 10")
True
>>> s.check("storage >= 0")
True
It is possible to evaluate how many steps it will take until a certain condition is met:
>>> stepsim.be_quiet()
>>> s.estimate_finish("storage == 2", 100)
8
Behind the scenes, this will run a copy of the simulation. A maximum step value will prevent hanging on impossible conditions:
>>> s.estimate_finish("cashbox < 1", 100)
100
Whe you remove a converter, its last step will be reverted. Note that this does not rewind the simulation step counter.
>>> stepsim.log_to_stdout()
>>> stepsim.loglevel("debug")
>>> s.step()
buyer: Conversion in progress, 2 steps left.
Active Container of buyer: None
>>> s.remove_converter("buyer")
reverting last draw from 'buyer'
buyer: returning 3 EUR to cashbox.
Removing converter 'buyer' from simulation.
Current containers: []
You can now step on through the simulation or simply let it run from the current state until an end condition is satisfied. In this case we let it run until the buyer can not buy any more parts:
>>> s.add_converter(buyer) Adding converter 'buyer' to simulation. Current containers: ['cashbox', 'storage'] >>> s.run(lambda : not buyer.last_step_successful) Starting simulation. --- Step 3: ----------------------------------------------- buyer: Ready to draw resources buyer: Drawing 3 EUR from cashbox. cashbox has 7 EUR left now. Active Container of buyer: <cashbox: 7 EUR in stock> --- Step 4: ----------------------------------------------- buyer: Conversion in progress, 2 steps left. Active Container of buyer: None --- Step 5: ----------------------------------------------- buyer: Conversion in progress, 1 steps left. Active Container of buyer: None --- Step 6: ----------------------------------------------- buyer: Delivering 1 parts to storage. storage stock is 1 parts now. Active Container of buyer: <storage: 1 parts in stock> --- Step 7: ----------------------------------------------- buyer: Ready to draw resources buyer: Drawing 3 EUR from cashbox. cashbox has 4 EUR left now. Active Container of buyer: <cashbox: 4 EUR in stock> --- Step 8: ----------------------------------------------- buyer: Conversion in progress, 2 steps left. Active Container of buyer: None --- Step 9: ----------------------------------------------- buyer: Conversion in progress, 1 steps left. Active Container of buyer: None --- Step 10: ----------------------------------------------- buyer: Delivering 1 parts to storage. storage stock is 2 parts now. Active Container of buyer: <storage: 2 parts in stock> --- Step 11: ----------------------------------------------- buyer: Ready to draw resources buyer: Drawing 3 EUR from cashbox. cashbox has 1 EUR left now. Active Container of buyer: <cashbox: 1 EUR in stock> --- Step 12: ----------------------------------------------- buyer: Conversion in progress, 2 steps left. Active Container of buyer: None --- Step 13: ----------------------------------------------- buyer: Conversion in progress, 1 steps left. Active Container of buyer: None --- Step 14: ----------------------------------------------- buyer: Delivering 1 parts to storage. storage stock is 3 parts now. Active Container of buyer: <storage: 3 parts in stock> --- Step 15: ----------------------------------------------- buyer: Ready to draw resources buyer: Cannot draw 3 EUR from cashbox, only 1 left. Active Container of buyer: None --- Break condition met, simulation finished. --------------- Final state after 15 steps: <cashbox: 1 EUR in stock> <storage: 3 parts in stock>
You can export the simulation graph in the DOT graph language (see http://www.graphviz.org/):
>>> s.save_dot("part_buyer.dot")
Writing DOT file.
digraph {
graph [size=5] ;
node [fontsize=10, fontname="Bitstream Vera Sans"] ;
"cashbox" [shape=box];
"cashbox" -> "buyer" ;
"storage" [shape=box];
"buyer" -> "storage" ;
}
<BLANKLINE>
Clean up:
>>> import os
>>> os.remove("part_buyer.dot")
The file ‘making_cakes.py’ shows a more elaborate example. It is included in the ZIP archive and will be installed in ‘share/doc/stepsim/examples’.
License
StepSim is licensed under the GPL. See the file COPYING for details.
