Well that pseudocode expresses our algorithm, but it is one vague, buggy mess at the moment. How to move from there to a clear, correct Python program? Let's start with a bit of OOP, and look for the nouns and verbs we've used in our pseudocode to identify the objects and methods we need to implement to let us express the algorithm.
The only objects in sight are Pitchers.
What attributes do they have? A capacity and some contents.
What methods do they have? fill and empty.
Any other verbs we've used? pour.
That leads directly to this code:
class Pitcher:
def __init__(self, capacity, contents=0):
self.capacity = capacity
self.contents = contents
def empty(self):
self.contents = 0
def fill(self):
self.contents = self.capacity
def __str__(self): # debugging aid
return '%d of %d' % (self.contents, self.capacity)
def pour(src, destn):
# How much can we pour into the destination pitcher?
destn_space = destn.capacity - destn.contents
# How much can we pour from the source pitcher?
src_avail = src.contents
# The amount we transfer is the least of those two amounts.
transfer = min(destn_space, src_avail)
#print 'Transferring', transfer, 'liters.'
# Now we simulate pouring by adjusting the amounts in each pitcher.
destn.contents += transfer
src.contents -= transfer
if __name__ == '__main__':
print 'Create pitchers 7:5 and 3:3'
a = Pitcher(7,5)
b = Pitcher(3,3)
print a
print b
print 'Try pouring into a full pitcher:'
pour(a,b)
print a
print b
print 'Try pouring from 3:3 into 7:5, should pour 2 litres:'
pour(b,a)
print a
print b
print 'Empty both pitchers:'
a.empty()
b.empty()
print a
print bRunning it produces some encouraging output:
>>>
Create pitchers 7:5 and 3:3
5 of 7
3 of 3
Try pouring into a full pitcher:
Transferring 0 litres.
5 of 7
3 of 3
Try pouring from 3:3 into 7:5, should pour 2 litres:
Transferring 2 litres.
7 of 7
1 of 3
Empty both pitchers:
0 of 7
0 of 3
>>>