创建子图时,Matplotlib"字典在迭代期间改变了大小"错误

Question

我写了一个函数,绘制了一个由两个不同大小的子图组成的图:

def draw_plot(data, function, sigma_value):

    gs = gridspec.GridSpec(1, 5)
    ax1 = subplot(gs[0, 0:3])  
    ax2 = subplot(gs[0, 3:5], sharey=ax1)                
    gs.update(wspace=0.05)
    ...

我应该提到这是一个模块级函数,因此在该模块的顶部我进行了导入

from pylab import *
import matplotlib.gridspec as gridspec

当我跑步时myplot.draw_plot(...),我明白了RuntimeError.事情是这种行为是不一致的.我可以调用该函数,比方说,三次,前两次我得到错误,而第三次运行OK.

追溯是

Traceback (most recent call last):
File "<interactive input>", line 1, in <module>
File "myplot.py", line 105, in draw_plot
    ax1 = subplot(gs[0, 0:3])                 
File "C:\Python32\lib\site-packages\matplotlib\pyplot.py", line 766, in subplot
    a = fig.add_subplot(*args, **kwargs)
File "C:\Python32\lib\site-packages\matplotlib\figure.py", line 779, in add_subplot
    a = subplot_class_factory(projection_class)(self, *args, **kwargs)
File "C:\Python32\lib\site-packages\matplotlib\axes.py", line 8380, in __init__
    self._axes_class.__init__(self, fig, self.figbox, **kwargs)
File "C:\Python32\lib\site-packages\matplotlib\axes.py", line 467, in __init__
    self.cla()
File "C:\Python32\lib\site-packages\matplotlib\axes.py", line 910, in cla
    self._shared_y_axes.clean()
File "C:\Python32\lib\site-packages\matplotlib\cbook.py", line 1493, in clean
    for key, val in mapping.items():
RuntimeError: dictionary changed size during iteration

谢谢你的帮助!

编辑

显然我一直试图弄清楚自己发生了什么,所以跟着Traceback我检查了clean()功能cbook.py.

def clean(self):
    """
    Clean dead weak references from the dictionary
    """
    mapping = self._mapping
    for key, val in mapping.items():
        if key() is None:
            del mapping[key]
            val.remove(key)

在函数中,我添加了一行可以打印mapping.items(),我注意到当这些项中有类似的条目时会发生错误<weakref at 0480EBA0; dead>.我完全不熟悉弱引用,所以我再次陷入困境.

编辑2 这当然不是一个好的解决方案,但注释掉clean()函数体有助于我的情况,而不会产生任何新的错误.

Answer 1

我刚刚发现最近的一篇文章Safely iterating over WeakKeyDictionary and WeakValueDictionary有助于解决非常类似的问题。

因此，使用 Bakuriu 给出的答案，我编辑了close()如下函数

def clean(self):
    """
    Clean dead weak references from the dictionary
    """

    mapping = self._mapping
    for key, val in list(mapping.items()):  # iterate over list now        
        if key() is None:
            del mapping[key]
            val.remove(key)

它似乎工作得很好！

编辑

我刚刚发现matplotlib该函数的新版本如下所示：

def clean(self):
    """
    Clean dead weak references from the dictionary
    """
    mapping = self._mapping
    to_drop = [key for key in mapping if key() is None]
    for key in to_drop:
        val = mapping.pop(key)
        val.remove(key)

来源：

https://github.com/matplotlib/matplotlib/blob/master/lib/matplotlib/cbook.py