Add steps argument to Predator Prey exercise code

Argument is mandatory, and requires a positive integer, previously defaulted to 250

Closes #83

Author: Robadob

episodes/files/pred-prey/predprey.py

@@ -415,8 +415,14 @@ def run(self, random_seed=12):
         # plot graph of results
         self._plot()
 
+# Argument parsing
+if len(sys.argv) != 2:
+    print("Script expects 1 positive integer argument (number of steps), %u found."%(len(sys.argv) - 1))
+    sys.exit()
+steps = int(sys.argv[1])
+if steps < 1:
+    print("Script expects 1 positive integer argument (number of steps), %s converts < 1."%(sys.argv[1]))
+    sys.exit()
 
-        
-        
-model = Model()
+model = Model(steps=steps)
 model.run()

episodes/profiling-functions.md

@@ -437,12 +437,11 @@ Download and profile <a href="files/pred-prey/predprey.py" download>the Python p
 >
 > The three agents; predators, prey and grass exist in a two dimensional grid. Predators eat prey, prey eat grass. The size of each population changes over time. Depending on the parameters of the model, the populations may oscillate, grow or collapse due to the availability of their food source.
 
-The program can be executed via `python predprey.py`.
+The program can be executed via `python predprey.py <steps>`.
+The value of `steps` for a full run is 250, however a full run may not be necessary to find the bottlenecks.
 
-It takes no arguments, but contains various environment properties which can be modified to change the model's behaviour.
 When the model finishes it outputs a graph of the three populations `predprey_out.png`.
 
-
 :::::::::::::::::::::::: solution 
 
 It should be clear from the profile that the method `Grass::eaten()` (from `predprey.py:278`) occupies the majority of the runtime.

episodes/profiling-lines.md

@@ -461,9 +461,10 @@ from line_profiler import profile
     def eaten(self, prey_list):
 ```
 
-`line_profiler` can then be executed via `python -m kernprof -lvr predprey.py`.
+`line_profiler` can then be executed via `python -m kernprof -lvr predprey.py <steps>`.
 
-This will take much longer to run due to `line_profiler`, you may wish to reduce the number of steps. In this instance it may change the profiling output slightly, as the number of `Prey` and their member variables evaluated by this method both change as the model progresses, but the overall pattern is likely to remain similar.
+This will take much longer to run due to `line_profiler`, you may wish profile less steps than you did in the function-level profiling exercise (250 was suggested for a full run).
+In this instance it may change the profiling output slightly, as the number of `Prey` and their member variables evaluated by this method both change as the model progresses, but the overall pattern is likely to remain similar.
 
 ```python
 # line ~420