事情是这样的：有朋友在学习用matplotlib作图，遇到一些问题问我，我也没用过，就想先装一个试试。然后呢，我就随手创建了个虚拟环境。结果，涉及到matplotlib的第一行就报错了：
Traceback (most recent call last):
File "D:/workspace/PyTest/get_data.py", line 22, in <module>
plt.scatter(X[:50, 0], X[:50, 1], color="red", marker="o", label="setosa")
File "D:\workspace\PyTest\py3env\lib\site-packages\matplotlib\pyplot.py", line 3420, in scatter
ax = gca()
File "D:\workspace\PyTest\py3env\lib\site-packages\matplotlib\pyplot.py", line 950, in gca
return gcf().gca(**kwargs)
File "D:\workspace\PyTest\py3env\lib\site-packages\matplotlib\pyplot.py", line 586, in gcf
return figure()
File "D:\workspace\PyTest\py3env\lib\site-packages\matplotlib\pyplot.py", line 535, in figure
**kwargs)
File "D:\workspace\PyTest\py3env\lib\site-packages\matplotlib\backends\backend_tkagg.py", line 81, in new_figure_manager
return new_figure_manager_given_figure(num, figure)
File "D:\workspace\PyTest\py3env\lib\site-packages\matplotlib\backends\backend_tkagg.py", line 89, in new_figure_manager_given_figure
window = Tk.Tk()
File "C:\Python35\Lib\tkinter\__init__.py", line 1868, in __init__
self.tk = _tkinter.create(screenName, baseName, className, interactive, wantobjects, useTk, sync, use)
_tkinter.TclError: Can't find a usable init.tcl in the following directories:
C:/Python35/lib/tcl8.6 D:/workspace/PyTest/py3env/lib/tcl8.6 D:/workspace/PyTest/lib/tcl8.6 D:/workspace/PyTest/py3env/library D:/workspace/PyTest/library D:/workspace/PyTest/tcl8.6.4/library D:/workspace/tcl8.6.4/library This probably means that Tcl wasn't installed properly.
经过分析，我想这是因为没有找到tkinter，而matplotlib需要用到这个。可是这东西装python时候是默认的，我肯定会装的。我翻了翻我的电脑，Tcl确实是装了的：
可是路径不对。经群里的同学指导，我还特意在主环境下测试了一下tk和tcl环境：
import tkinter
root = tkinter.Tk()
print(root.tk.exprstring('$tcl_library'))
print(root.tk.exprstring('$tk_library'))
在主环境中结果也是正常的：
C:\Python35\tcl\tcl8.6
C:/Python35/tcl/tk8.6
可是虚拟环境中就不正常了。
Traceback (most recent call last):
File "D:/workspace/PyTest/testtk.py", line 2, in <module>
root = tkinter.Tk()
File "C:\Python35\Lib\tkinter\__init__.py", line 1868, in __init__
self.tk = _tkinter.create(screenName, baseName, className, interactive, wantobjects, useTk, sync, use)
_tkinter.TclError: Can't find a usable init.tcl in the following directories:
C:/Python35/lib/tcl8.6 D:/workspace/PyTest/py3env/lib/tcl8.6 D:/workspace/PyTest/lib/tcl8.6 D:/workspace/PyTest/py3env/library D:/workspace/PyTest/library D:/workspace/PyTest/tcl8.6.4/library D:/workspace/tcl8.6.4/library This probably means that Tcl wasn't installed properly.
这可就尴尬了。
但是，我又注意到一个细节：Tcl在查找环境的时候，会查找本机的主python环境，比如刚才那段报错中，Tcl查找了这样两个环境：
C:/Python35/lib/tcl8.6
D:/workspace/PyTest/py3env/lib/tcl8.6
其中C盘是我的主环境，D:/workspace/PyTest/py3env是虚拟环境。
然后我开始翻代码，看tcl查询的路径是啥。找不到。网上介绍了添加环境变量，TCL_LIBRARY和TK_LIBRARY，我试了也不行（可能这两个变量仅限于Linux系统），在path里面添加也不行。
走投无路的情况下我开始动歪脑筋，把Tcl8.6整个文件夹从C:\Python35\tcl\复制到了C:\Python35\Lib中，然后，居然……
Traceback (most recent call last):
File "D:/workspace/PyTest/ML/mcpperceptron/get_data.py", line 22, in <module>
plt.scatter(X[:50, 0], X[:50, 1], color="red", marker="o", label="setosa")
File "D:\workspace\PyTest\py3env\lib\site-packages\matplotlib\pyplot.py", line 3420, in scatter
ax = gca()
File "D:\workspace\PyTest\py3env\lib\site-packages\matplotlib\pyplot.py", line 950, in gca
return gcf().gca(**kwargs)
File "D:\workspace\PyTest\py3env\lib\site-packages\matplotlib\pyplot.py", line 586, in gcf
return figure()
File "D:\workspace\PyTest\py3env\lib\site-packages\matplotlib\pyplot.py", line 535, in figure
**kwargs)
File "D:\workspace\PyTest\py3env\lib\site-packages\matplotlib\backends\backend_tkagg.py", line 81, in new_figure_manager
return new_figure_manager_given_figure(num, figure)
File "D:\workspace\PyTest\py3env\lib\site-packages\matplotlib\backends\backend_tkagg.py", line 89, in new_figure_manager_given_figure
window = Tk.Tk()
File "C:\Python35\Lib\tkinter\__init__.py", line 1868, in __init__
self.tk = _tkinter.create(screenName, baseName, className, interactive, wantobjects, useTk, sync, use)
_tkinter.TclError: Can't find a usable tk.tcl in the following directories:
C:/Python35/lib/tcl8.6/tk8.6 C:/Python35/lib/tk8.6 D:/workspace/PyTest/py3env/lib/tk8.6 D:/workspace/PyTest/lib/tk8.6 D:/workspace/PyTest/py3env/library This probably means that tk wasn't installed properly.
报的错从“找不到Tcl”变成了“找不到Tk”！
难道说成功了？于是，我又如法炮制，把tk8.6文件夹从C:\Python35\tcl\复制到了C:\Python35\Lib\tcl8.6中。
然后就真的成功了！
这叫什么鬼问题嘛！╭(╯^╰)╮
好吧，就是提醒注意一下，在windows中的虚拟环境下，如果使用tk，注意tcl和tk的路径。可以把整个目录复制到tcl和tk的搜索路径中。至于这叫什么操作，我也不知道。