Introduce sim example

python/examples/sim.py

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+# standard imports
+import logging
+
+# local imports
+from erc20_demurrage_token import DemurrageTokenSettings
+from erc20_demurrage_token.sim import DemurrageTokenSimulation
+
+logging.basicConfig(level=logging.WARNING)
+logg = logging.getLogger()
+
+decay_per_minute = 0.000050105908373373 # equals approx 2% per month
+
+# parameters for simulation object
+settings = DemurrageTokenSettings()
+settings.name = 'Simulated Demurrage Token'
+settings.symbol = 'SIM'
+settings.decimals = 6
+settings.demurrage_level = int(decay_per_minute*(10**40))
+settings.period_minutes = 10800 # 1 week in minutes
+chain = 'evm:foochain:42'
+cap = sim.from_units(10 ** 12) # 1 tn token units, with 6 decimal places
+
+# instantiate simulation
+sim = DemurrageTokenSimulation(chain, settings, redistribute=True, cap=cap, actors=10)
+
+# name the usual suspects
+alice = sim.actors[0]
+bob = sim.actors[1]
+carol = sim.actors[2]
+
+# mint and transfer (every single action advances one block, and one second in time)
+sim.mint(alice, sim.from_units(100)) # 10000000 tokens
+sim.mint(bob, sim.from_units(100))
+sim.transfer(alice, carol, sim.from_units(50))
+
+# check that balances have been updated
+assert sim.balance(alice) == sim.from_units(50)
+assert sim.balance(bob) == sim.from_units(100)
+assert sim.balance(carol) == sim.from_units(50)
+
+# advance to next redistribution period
+sim.next()
+
+# inspect balances
+print('alice balance: demurraged {:>9d} base {:>9d}'.format(sim.balance(alice), sim.balance(alice, base=True)))
+print('bob balance:   demurraged {:>9d} base {:>9d}'.format(sim.balance(bob), sim.balance(bob, base=True)))
+print('carol balance: demurraged {:>9d} base {:>9d}'.format(sim.balance(carol), sim.balance(carol, base=True)))
+
+
+# get times
+minutes = sim.get_minutes()
+start = sim.get_now()
+timestamp = sim.get_start()
+period = sim.get_period()
+print('start {} now {} period {} minutes passed {}'.format(start, timestamp, period, minutes))
+
+
+contract_demurrage = 1 - sim.get_demurrage_modifier()    # demurrage in percent (float)
+frontend_demurrage = ((1 - decay_per_minute) ** minutes / 100)   # corresponding demurrage modifier (float)
+demurrage_delta = contract_demurrage - frontend_demurrage      # difference between demurrage in contract and demurrage calculated in frontend
+
+alice_checksum = 50000000 - (50000000 * frontend_demurrage) + (200000000 * frontend_demurrage) # alice's balance calculated with frontend demurrage
+print("""alice frontend balance {}
+alice contract balance {}
+frontend demurrage {}
+contract demurrage {}
+demurrage delta {}""".format(
+    alice_checksum,
+    sim.balance(alice),
+    frontend_demurrage,
+    contract_demurrage,
+    demurrage_delta),
+)
+
+balance_sum = sim.balance(alice) + sim.balance(bob) + sim.balance(carol)
+print('sum of contract demurraged balances {}'.format(balance_sum))