<p>首先,编写一些代码来重新创建示例:</p>
<pre><code>import random
class Event(object):
def __init__(self):
self.car = None
class Car(object):
def __init__(self, isBlue, length):
self._isBlue = isBlue
self._length = length
def isBlue(self):
return self._isBlue
def length(self):
return self._length
def __str__(self):
return '{} car of {} m long.'.format('blue' if self.isBlue() else 'non-blue ', self.length())
</code></pre>
<p>好的,现在我随机创建十个<code>car</code>对象并将它们添加到<code>event</code>:</p>
<pre><code>totalNumberOfCars = 10
events = []
for _ in range(totalNumberOfCars):
car = Car(random.choice([True, False]), random.randrange(5, 40)/10.)
print car
event = Event()
event.car = car
events.append(event)
</code></pre>
<p>对我来说,输出如下(您的输出当然可以不同):</p>
<pre><code>blue car of 0.5 m long.
non-blue car of 2.3 m long.
non-blue car of 3.8 m long.
blue car of 2.1 m long.
non-blue car of 0.6 m long.
blue car of 0.8 m long.
blue car of 0.5 m long.
blue car of 2.3 m long.
blue car of 3.3 m long.
blue car of 2.1 m long.
</code></pre>
<p>现在,如果我们想按地区统计我们的事件,您可以按以下步骤进行:</p>
<pre><code>allBlueCars = sum(1 for event in events if event.car.isBlue())
print "Number of blue cars: {}".format(allBlueCars)
maxCarLen = 4
for region in zip(range(maxCarLen ), range(1, maxCarLen +1)):
minlen, maxlen = region
print "Cars between {} and {} m that are blue:".format(minlen, maxlen)
blueCarsInRegion = [str(event.car) for event in events if event.car.isBlue() and minlen <= event.car.length() < maxlen]
if blueCarsInRegion:
print '\n'.join(['\t{}'.format(car) for car in blueCarsInRegion])
else:
print 'no blue cars in this region'
fraction = float(len(blueCarsInRegion)) / allBlueCars
print "fraction of cars that are blue and between {} and {} m long: {}".format(minlen, maxlen, fraction)
print
</code></pre>
<p>对于上述示例数据,将打印:</p>
<pre><code>Number of blue cars: 7
Cars between 0 and 1 m that are blue:
blue car of 0.5 m long.
blue car of 0.8 m long.
blue car of 0.5 m long.
fraction of cars that are blue and between 0 and 1 m long: 0.428571428571
Cars between 1 and 2 m that are blue:
no blue cars in this region
fraction of cars that are blue and between 1 and 2 m long: 0.0
Cars between 2 and 3 m that are blue:
blue car of 2.1 m long.
blue car of 2.3 m long.
blue car of 2.1 m long.
fraction of cars that are blue and between 2 and 3 m long: 0.428571428571
Cars between 3 and 4 m that are blue:
blue car of 3.3 m long.
fraction of cars that are blue and between 3 and 4 m long: 0.142857142857
</code></pre>