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280 lines
26 KiB
Markdown
280 lines
26 KiB
Markdown
# super() 函数
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```py
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super(CurrentClassName, instance)
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```
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返回该类实例对应的父类对象。
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In [1]:
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```py
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class Leaf(object):
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def __init__(self, color="green"):
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self.color = color
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def fall(self):
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print "Splat!"
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class MapleLeaf(Leaf):
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def change_color(self):
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if self.color == "green":
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self.color = "red"
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def fall(self):
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self.change_color()
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super(MapleLeaf, self).fall()
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```
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这里，我们先改变树叶的颜色，然后再找到这个实例对应的父类，并调用父类的 `fall()` 方法：
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In [2]:
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```py
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mleaf = MapleLeaf()
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print mleaf.color
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mleaf.fall()
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print mleaf.color
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```
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```py
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green
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Splat!
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red
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```
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回到我们的森林例子，这里我们将森林 `Forest` 作为父类，并定义一个子类 `BurnableForest`：
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In [3]:
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```py
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import numpy as np
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class Forest(object):
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""" Forest can grow trees which eventually die."""
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def __init__(self, size=(150,150), p_sapling=0.0025):
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self.size = size
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self.trees = np.zeros(self.size, dtype=bool)
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self.p_sapling = p_sapling
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def __repr__(self):
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my_repr = "{}(size={})".format(self.__class__.__name__, self.size)
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return my_repr
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def __str__(self):
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return self.__class__.__name__
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@property
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def num_cells(self):
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"""Number of cells available for growing trees"""
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return np.prod(self.size)
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@property
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def tree_fraction(self):
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"""
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Fraction of trees
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"""
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num_trees = self.trees.sum()
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return float(num_trees) / self.num_cells
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def _rand_bool(self, p):
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"""
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Random boolean distributed according to p, less than p will be True
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"""
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return np.random.uniform(size=self.trees.shape) < p
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def grow_trees(self):
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"""
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Growing trees.
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"""
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growth_sites = self._rand_bool(self.p_sapling)
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self.trees[growth_sites] = True
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def advance_one_step(self):
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"""
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Advance one step
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"""
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self.grow_trees()
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```
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* 将与燃烧相关的属性都被转移到了子类中去。
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* 修改两类的构造方法，将闪电概率放到子类的构造方法上，同时在子类的构造方法中，用 `super` 调用父类的构造方法。
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* 修改 `advance_one_step()`，父类中只进行生长，在子类中用 `super` 调用父类的 `advance_one_step()` 方法，并添加燃烧的部分。
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In [4]:
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```py
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class BurnableForest(Forest):
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"""
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Burnable forest support fires
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"""
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def __init__(self, p_lightning=5.0e-6, **kwargs):
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super(BurnableForest, self).__init__(**kwargs)
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self.p_lightning = p_lightning
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self.fires = np.zeros((self.size), dtype=bool)
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def advance_one_step(self):
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"""
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Advance one step
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"""
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super(BurnableForest, self).advance_one_step()
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self.start_fires()
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self.burn_trees()
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@property
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def fire_fraction(self):
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"""
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Fraction of fires
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"""
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num_fires = self.fires.sum()
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return float(num_fires) / self.num_cells
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def start_fires(self):
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"""
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Start of fire.
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"""
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lightning_strikes = (self._rand_bool(self.p_lightning) &
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self.trees)
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self.fires[lightning_strikes] = True
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def burn_trees(self):
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"""
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Burn trees.
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"""
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fires = np.zeros((self.size[0] + 2, self.size[1] + 2), dtype=bool)
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fires[1:-1, 1:-1] = self.fires
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north = fires[:-2, 1:-1]
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south = fires[2:, 1:-1]
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east = fires[1:-1, :-2]
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west = fires[1:-1, 2:]
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new_fires = (north | south | east | west) & self.trees
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self.trees[self.fires] = False
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self.fires = new_fires
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```
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测试父类：
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In [5]:
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```py
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forest = Forest()
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forest.grow_trees()
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print forest.tree_fraction
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```
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```py
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0.00284444444444
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```
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测试子类：
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In [6]:
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```py
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burnable_forest = BurnableForest()
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```
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调用自己和父类的方法：
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In [7]:
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```py
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burnable_forest.grow_trees()
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burnable_forest.start_fires()
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burnable_forest.burn_trees()
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print burnable_forest.tree_fraction
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```
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```py
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0.00235555555556
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```
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查看变化：
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In [8]:
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```py
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import matplotlib.pyplot as plt
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%matplotlib inline
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forest = Forest()
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forest2 = BurnableForest()
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tree_fractions = []
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for i in range(2500):
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forest.advance_one_step()
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forest2.advance_one_step()
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tree_fractions.append((forest.tree_fraction, forest2.tree_fraction))
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plt.plot(tree_fractions)
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plt.show()
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```
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`__str__` 和 `__repr__` 中 `self.__class__` 会根据类型不同而不同：
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In [9]:
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```py
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forest
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```
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Out[9]:
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```py
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Forest(size=(150, 150))
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```
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In [10]:
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```py
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forest2
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```
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Out[10]:
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```py
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BurnableForest(size=(150, 150))
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```
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In [11]:
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```py
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print forest
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```
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```py
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Forest
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```
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In [12]:
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```py
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print forest2
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```
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```py
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BurnableForest
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``` |