在Python中使用matplotlib设置刻度位置时出错

Question

我正在尝试在matplotlib中设置刻度标记的位置。运行下面这个简单的例子时，我遇到了错误：

import matplotlib.pyplot as plt
import numpy as np
from matplotlib.ticker import MultipleLocator

x = 10.*np.random.randn(1000)
y = 10.*np.random.randn(1000)

fig = plt.figure()
ax = fig.add_subplot(1,1,1)
ax.scatter(x, y)
ax.xaxis.set_major_formatter(MultipleLocator(1.))
ax.yaxis.set_major_formatter(MultipleLocator(1.))
plt.show()

错误出现在设置x轴和y轴刻度标记的那两行。如果我用NullFormatter()代替，或者干脆省略这两行，代码就能正常运行，并且生成预期的图表。不过，上面的代码却返回了以下错误：

Exception in Tkinter callback
Traceback (most recent call last):
  File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 1413, in __call__
    return self.func(*args)
  File "/usr/lib/pymodules/python2.7/matplotlib/backends/backend_tkagg.py", line 245, in resize
    self.show()
  File "/usr/lib/pymodules/python2.7/matplotlib/backends/backend_tkagg.py", line 248, in draw
    FigureCanvasAgg.draw(self)
  File "/usr/lib/pymodules/python2.7/matplotlib/backends/backend_agg.py", line 394, in draw
    self.figure.draw(self.renderer)
  File "/usr/lib/pymodules/python2.7/matplotlib/artist.py", line 55, in draw_wrapper
    draw(artist, renderer, *args, **kwargs)
  File "/usr/lib/pymodules/python2.7/matplotlib/figure.py", line 798, in draw
    func(*args)
  File "/usr/lib/pymodules/python2.7/matplotlib/artist.py", line 55, in draw_wrapper
    draw(artist, renderer, *args, **kwargs)
  File "/usr/lib/pymodules/python2.7/matplotlib/axes.py", line 1946, in draw
    a.draw(renderer)
  File "/usr/lib/pymodules/python2.7/matplotlib/artist.py", line 55, in draw_wrapper
    draw(artist, renderer, *args, **kwargs)
  File "/usr/lib/pymodules/python2.7/matplotlib/axis.py", line 971, in draw
    tick_tups = [ t for t in self.iter_ticks()]
  File "/usr/lib/pymodules/python2.7/matplotlib/axis.py", line 906, in iter_ticks
    self.major.formatter.set_locs(majorLocs)
AttributeError: MultipleLocator instance has no attribute 'set_locs'

我试着在网上搜索这个错误，但找不到其他人有类似的问题。有没有人知道为什么使用定位器会导致错误呢？

Answer 1

MultipleLocator 是一个定位器，而不是格式化工具。你应该使用

ax.xaxis.set_major_locator(MultipleLocator(1.))
ax.yaxis.set_major_locator(MultipleLocator(1.))

这个对我来说有效（虽然用1看起来不太好，但确实有效）。