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path直接指向graphviz安装路径
            path = r"C:\Program Files (x86)\Graphviz2.38\bin"

        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