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160 lines
2.4 KiB
Markdown
160 lines
2.4 KiB
Markdown
# 定义 class
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## 基本形式
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`class` 定义如下：
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```py
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class ClassName(ParentClass):
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"""class docstring"""
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def method(self):
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return
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```
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* `class` 关键词在最前面
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* `ClassName` 通常采用 `CamelCase` 记法
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* 括号中的 `ParentClass` 用来表示继承关系
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* 冒号不能缺少
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* `""""""` 中的内容表示 `docstring`，可以省略
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* 方法定义与函数定义十分类似，不过多了一个 `self` 参数表示这个对象本身
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* `class` 中的方法要进行缩进
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In [1]:
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```py
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class Forest(object):
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""" Forest can grow trees which eventually die."""
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pass
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```
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其中 `object` 是最基本的类型。
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查看帮助：
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In [2]:
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```py
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import numpy as np
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np.info(Forest)
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```
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```py
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Forest()
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Forest can grow trees which eventually die.
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Methods:
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```
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In [3]:
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```py
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forest = Forest()
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```
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In [4]:
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```py
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forest
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```
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Out[4]:
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```py
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<__main__.Forest at 0x3cda358>
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```
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## 添加方法和属性
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可以直接添加属性（有更好的替代方式）：
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In [5]:
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```py
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forest.trees = np.zeros((150, 150), dtype=bool)
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```
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In [6]:
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```py
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forest.trees
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```
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Out[6]:
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```py
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array([[False, False, False, ..., False, False, False],
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[False, False, False, ..., False, False, False],
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[False, False, False, ..., False, False, False],
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...,
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[False, False, False, ..., False, False, False],
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[False, False, False, ..., False, False, False],
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[False, False, False, ..., False, False, False]], dtype=bool)
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```
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In [7]:
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```py
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forest2 = Forest()
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```
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`forest2` 没有这个属性：
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In [8]:
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```py
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forest2.trees
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```
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```py
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---------------------------------------------------------------------------
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AttributeError Traceback (most recent call last)
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<ipython-input-8-42e6a9d57a8b> in <module>()
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----> 1 forest2.trees
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AttributeError: 'Forest' object has no attribute 'trees'
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```
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添加方法时，默认第一个参数是对象本身，一般为 `self`，可能用到也可能用不到，然后才是其他的参数：
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In [9]:
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```py
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class Forest(object):
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""" Forest can grow trees which eventually die."""
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def grow(self):
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print "the tree is growing!"
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def number(self, num=1):
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if num == 1:
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print 'there is 1 tree.'
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else:
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print 'there are', num, 'trees.'
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```
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In [10]:
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```py
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forest = Forest()
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forest.grow()
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forest.number(12)
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```
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```py
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the tree is growing!
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there are 12 trees.
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``` |