Merge pull request #74 from realpython/simpy

Simpy

Author: jayascript

simulation-with-simpy/README.md

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+# Simulating Real-World Processes With SimPy
+
+Corresponding code for ["Simulating Real-World Processes With SimPy."](https://realpython.com/simulation-with-simpy/)
+
+## Running the Script
+
+The file `simulate.py` contains the script that mimics the tutorial code. You can execute the code by running `python3 simulate.py` from the directory that contains the file.
+
+Here is some sample output:
+
+```console
+$ python3 simulate.py
+Input # of cashiers working: 1
+Input # of servers working: 1
+Input # of ushers working: 1
+Running simulation...
+The average wait time is 42 minutes and 26 seconds.
+```

simulation-with-simpy/simulate.py

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+"""Companion code to https://realpython.com/simulation-with-simpy/
+
+'Simulating Real-World Processes With SimPy'
+
+Python version: 3.7.3
+SimPy version: 3.0.11
+"""
+
+import simpy
+import random
+import statistics
+
+wait_times = []
+
+
+class Theater(object):
+    def __init__(self, env, num_cashiers, num_servers, num_ushers):
+        self.env = env
+        self.cashier = simpy.Resource(env, num_cashiers)
+        self.server = simpy.Resource(env, num_servers)
+        self.usher = simpy.Resource(env, num_ushers)
+
+    def purchase_ticket(self, moviegoer):
+        yield self.env.timeout(random.randint(1, 3))
+
+    def check_ticket(self, moviegoer):
+        yield self.env.timeout(3 / 60)
+
+    def sell_food(self, moviegoer):
+        yield self.env.timeout(random.randint(1, 5))
+
+
+def go_to_movies(env, moviegoer, theater):
+    # Moviegoer arrives at the theater
+    arrival_time = env.now
+
+    with theater.cashier.request() as request:
+        yield request
+        yield env.process(theater.purchase_ticket(moviegoer))
+
+    with theater.usher.request() as request:
+        yield request
+        yield env.process(theater.check_ticket(moviegoer))
+
+    if random.choice([True, False]):
+        with theater.server.request() as request:
+            yield request
+            yield env.process(theater.sell_food(moviegoer))
+
+    # Moviegoer heads into the theater
+    wait_times.append(env.now - arrival_time)
+
+
+def run_theater(env, num_cashiers, num_servers, num_ushers):
+    theater = Theater(env, num_cashiers, num_servers, num_ushers)
+
+    for moviegoer in range(3):
+        env.process(go_to_movies(env, moviegoer, theater))
+
+    while True:
+        yield env.timeout(0.20)  # Wait a bit before generating a new person
+
+        moviegoer += 1
+        env.process(go_to_movies(env, moviegoer, theater))
+
+
+def get_average_wait_time(wait_times):
+    average_wait = statistics.mean(wait_times)
+    # Pretty print the results
+    minutes, frac_minutes = divmod(average_wait, 1)
+    seconds = frac_minutes * 60
+    return round(minutes), round(seconds)
+
+
+def get_user_input():
+    num_cashiers = input("Input # of cashiers working: ")
+    num_servers = input("Input # of servers working: ")
+    num_ushers = input("Input # of ushers working: ")
+    params = [num_cashiers, num_servers, num_ushers]
+    if all(str(i).isdigit() for i in params):  # Check input is valid
+        params = [int(x) for x in params]
+    else:
+        print(
+            "Could not parse input. Simulation will use default values:",
+            "\n1 cashier, 1 server, 1 usher.",
+        )
+        params = [1, 1, 1]
+    return params
+
+
+def main():
+    # Setup
+    random.seed(42)
+    num_cashiers, num_servers, num_ushers = get_user_input()
+
+    # Run the simulation
+    env = simpy.Environment()
+    env.process(run_theater(env, num_cashiers, num_servers, num_ushers))
+    env.run(until=90)
+
+    # View the results
+    mins, secs = get_average_wait_time(wait_times)
+    print(
+        "Running simulation...",
+        f"\nThe average wait time is {mins} minutes and {secs} seconds.",
+    )
+
+
+if __name__ == "__main__":
+    main()