theano 0.8与pydot、graphziv的冲突解决

在python中import theano时，如果出现Couldn't import dot_parser, loading of dot files will not be possible.之类的错误，可以按如下步骤解决

1. pip uninstall pydot pyparsing graphviz

2.如果是window，先安装graphviz-2.38.msi;如果是Ubuntu系统，则apt-get install graphviz，并将graphviz的bin目录的路径添加到系统PATH变量中

3.pip install graphviz

4.pip install pyparsing==2.0.1

4.pip install pydot

经此几个步骤后，应该就可以正常使用theano和pydot等库文件了。如果还是无法正确找到graphviz的可执行文件，则采用第二种方法：

在Python的安装目录中找到Lib\site-packages\pydot.py文件，手动修改pydot.find_graphviz()函数，例如我是这样改的：

def find_graphviz():    """Locate Graphviz's executables in the system.    Tries three methods:    First: Windows Registry (Windows only)    This requires Mark Hammond's pywin32 is installed.    Secondly: Search the path    It will look for 'dot', 'twopi' and 'neato' in all the directories    specified in the PATH environment variable.    Thirdly: Default install location (Windows only)    It will look for 'dot', 'twopi' and 'neato' in the default install    location under the "Program Files" directory.    It will return a dictionary containing the program names as keys    and their paths as values.    If this fails, it returns None.    """    # Method 1 (Windows only)    ##=======================注释掉这部分内容，不在这个if内搜索graphviz安装目录================#     if os.sys.platform == 'win32':#     #         try:#             import win32api, win32con#             #             # Get the GraphViz install path from the registry#             ##             hkey = win32api.RegOpenKeyEx( win32con.HKEY_LOCAL_MACHINE,#                 "SOFTWARE\ATT\Graphviz", 0, win32con.KEY_QUERY_VALUE )#                 #             path = win32api.RegQueryValueEx( hkey, "InstallPath" )[0]#             win32api.RegCloseKey( hkey )#             #             # Now append the "bin" subdirectory:#             ##             path = os.path.join(path, "bin")#             progs = __find_executables(path)#             if progs is not None :#                 #print "Used Windows registry"#                 return progs#                 #         except ImportError :#             # Print a messaged suggesting they install these?#             ##             pass# #==============================================================================    # Method 2 (Linux, Windows etc)    #    if os.environ.has_key('PATH'):        for path in os.environ['PATH'].split(os.pathsep):            progs = __find_executables(path)            if progs is not None :                #print "Used path"                return progs    # Method 3 (Windows only)    #    if os.sys.platform == 'win32':        # Try and work out the equivalent of "C:\Program Files" on this        # machine (might be on drive D:, or in a different language)        #        if os.environ.has_key('PROGRAMFILES'):            # Note, we could also use the win32api to get this            # information, but win32api may not be installed.            path = os.path.join(os.environ['PROGRAMFILES'], 'ATT', 'GraphViz', 'bin')        else:            #Just in case, try the default...,修改此次，将<span style="line-height: 26px; font-family: 'microsoft yahei';">path直接指向graphviz安装路径</span>            <span style="color:#ff0000;">path = r"C:\Program Files (x86)\Graphviz2.38\bin"</span>        progs = __find_executables(path)        if progs is not None :            #print "Used default install location"            return progs    progs = __find_executables(path)    if progs is not None :        #print "Used default install location"        return progs    for path in (        '/usr/bin', '/usr/local/bin',        '/opt/bin', '/sw/bin', '/usr/share',        '/Applications/Graphviz.app/Contents/MacOS/' ):        progs = __find_executables(path)        if progs is not None :            #print "Used path"            return progs    # Failed to find GraphViz    #    return None