有一類matplotlib.axes.AxesSubplot，但模塊matplotlib.axes有沒有屬性AxesSubplot

Question

代碼

import matplotlib.pyplot as plt 
fig = plt.figure() 
ax = fig.add_subplot(111) 
print type(ax) 

給出輸出

<class 'matplotlib.axes.AxesSubplot'> 

然後代碼

import matplotlib.axes 
matplotlib.axes.AxesSubplot 

引發異常

AttributeError: 'module' object has no attribute 'AxesSubplot' 

總之，有一個類matplotlib.axes.AxesSubplot，但模塊matplotlib.axes沒有屬性AxesSubplot。究竟是怎麼回事？

我正在使用Matplotlib 1.1.0和Python 2.7.3。

Answer 1

嘿。那是因爲是沒有AxesSubplot類..直到有一個需要時，當一個從SubplotBase構建。這是通過一些魔法axes.py完成：

def subplot_class_factory(axes_class=None): 
    # This makes a new class that inherits from SubplotBase and the 
    # given axes_class (which is assumed to be a subclass of Axes). 
    # This is perhaps a little bit roundabout to make a new class on 
    # the fly like this, but it means that a new Subplot class does 
    # not have to be created for every type of Axes. 
    if axes_class is None: 
     axes_class = Axes 

    new_class = _subplot_classes.get(axes_class) 
    if new_class is None: 
     new_class = new.classobj("%sSubplot" % (axes_class.__name__), 
           (SubplotBase, axes_class), 
           {'_axes_class': axes_class}) 
     _subplot_classes[axes_class] = new_class 

    return new_class 

因此它在飛行中做出，但它的SubplotBase一個子類：

>>> import matplotlib.pyplot as plt 
>>> fig = plt.figure() 
>>> ax = fig.add_subplot(111) 
>>> print type(ax) 
<class 'matplotlib.axes.AxesSubplot'> 
>>> b = type(ax) 
>>> import matplotlib.axes 
>>> issubclass(b, matplotlib.axes.SubplotBase) 
True