Added Item_19

Author: craigem

item_19.py

@@ -0,0 +1,86 @@
+#!/usr/bin/env python3
+
+'''Item 19 from Effective Python'''
+
+
+# Example 1
+''' calling a function in Python allows for passing arguments by position '''
+print('Example 1:\n==========')
+
+def remainder(number, divisor):
+    return number % divisor
+
+assert remainder(20, 7) == 6
+
+
+# Example 2
+''' The keyword arguments can be passed in any order as long as all of the
+required positional arguments are specified. You can mix and match keyword and
+positional arguments. These calls are equivalent '''
+print('\nExample 2:\n==========')
+
+remainder(20, 7)
+remainder(20, divisor=7)
+remainder(number=20, divisor=7)
+remainder(divisor=7, number=20)
+
+
+# Example 3
+''' compute the rate of fluid flowing into a vat. If the vat is also on a
+scale, then you could use the difference between two weight measurements at two
+different times to deter- mine the flow rate '''
+print('\nExample 3:\n==========')
+
+def flow_rate(weight_diff, time_diff):
+    return weight_diff / time_diff
+
+weight_diff = 0.5
+time_diff = 3
+flow = flow_rate(weight_diff, time_diff)
+print('%.3f kg per second' % flow)
+
+
+# Example 4
+''' it'd be helpful to use the last sensor measurements to approximate larger
+time scales, like hours or days. You can provide this behavior in the same
+function by adding an argument for the time period scaling factor '''
+print('\nExample 4:\n==========')
+
+def flow_rate(weight_diff, time_diff, period):
+    return (weight_diff / time_diff) * period
+
+flow_per_second = flow_rate(weight_diff, time_diff, 1)
+print('Flow per second: %s kg' % flow_per_second)
+
+
+# Example 5
+''' To make this less noisy, I can give the period argument a default value '''
+print('\nExample 5:\n==========')
+
+def flow_rate(weight_diff, time_diff, period=1):
+    return (weight_diff / time_diff) * period
+
+flow_per_second = flow_rate(weight_diff, time_diff)
+flow_per_hour = flow_rate(weight_diff, time_diff, period=3600)
+print('Flow per second: %s kg' % flow_per_second)
+print('Flow per hour: %s kg' % flow_per_hour)
+
+
+# Example 6
+''' extend the flow_rate function above to calculate flow rates in weight units
+besides kilograms '''
+print('\nExample 6:\n==========')
+
+def flow_rate(weight_diff, time_diff, period=1, units_per_kg=1):
+    return ((weight_diff * units_per_kg) / time_diff) * period
+
+pounds_per_hour = flow_rate(weight_diff, time_diff, period=3600,
+                            units_per_kg=2.2)
+
+
+# Example 7
+''' The only problem with this approach is that optional keyword ­arguments
+like period and units_per_kg may still be specified as positional arguments '''
+print('\nExample 7:\n==========')
+
+pounds_per_hour = flow_rate(weight_diff, time_diff, 3600, 2.2)