重定义 __init__

Question

我有一个来自某个库的类，我想修改这个类的构造函数的行为。

我正在做：

from library import TheClass

TheClass._original_init = TheClass.__init__

def f(self, *karg, **kargw):
  print "hello"
  self._original_init(*karg, **kargw)

TheClass.__init__ = f

这样做是对的吗？在这个特定情况下，我遇到了问题：

import matplotlib.pyplot as plt
from matplotlib import axes
from matplotlib.ticker import MultipleLocator

axes.Subplot._original_init = axes.Subplot.__init__ 

def f(self, *karg, **kargw):
    def add_minor_locator(axis, n = 5):
        ticklocs = axis.get_ticklocs()
        diff = ticklocs[1] - ticklocs[0]
        minorLocator = MultipleLocator(diff/float(n))
        axis.set_minor_locator(minorLocator)
    add_minor_locator(self.get_xaxis())
    add_minor_locator(self.get_yaxis())

    self._original_init(*karg, **kargw)

axes.Subplot.__init__ = f

fig, ax = plt.subplots(nrows=1, ncols=1)

我得到了：

  File "/usr/lib64/python2.7/site-packages/matplotlib/axes.py", line 1319, in get_xaxis
    return self.xaxis
AttributeError: 'AxesSubplot' object has no attribute 'xaxis'

Answer 1

你假设原来的 __init__ 方法已经执行过了；self.get_xaxis() 这个方法应该只在初始化完成后才可以调用：

def f(self, *karg, **kargw):
    _original_init(self, *karg, **kargw)

    def add_minor_locator(axis, n = 5):
        ticklocs = axis.get_ticklocs()
        diff = ticklocs[1] - ticklocs[0]
        minorLocator = MultipleLocator(diff/float(n))
        axis.set_minor_locator(minorLocator)
    add_minor_locator(self.get_xaxis())
    add_minor_locator(self.get_yaxis())