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)
    #
    if os.sys.platform == 'win32':
        
        HKEY_LOCAL_MACHINE =    0x80000002
        KEY_QUERY_VALUE =       0x0001

        RegOpenKeyEx = None
        RegQueryValueEx = None
        RegCloseKey = None
        
        try:
            import win32api, win32con
            RegOpenKeyEx = win32api.RegOpenKeyEx
            RegQueryValueEx = win32api.RegQueryValueEx
            RegCloseKey = win32api.RegCloseKey

        except ImportError:
            # Print a messaged suggesting they install these?
            #
            pass

        try:
            import ctypes
            
            def RegOpenKeyEx(key, subkey, opt, sam):
                result = ctypes.c_uint(0)
                ctypes.windll.advapi32.RegOpenKeyExA(key, subkey, opt, sam, ctypes.byref(result))
                return result.value
                
            def RegQueryValueEx( hkey, valuename ):
                data_type = ctypes.c_uint(0)
                data_len = ctypes.c_uint(1024)
                data = ctypes.create_string_buffer( 1024 )
                
                res = ctypes.windll.advapi32.RegQueryValueExA(hkey, valuename, 0, 
                    ctypes.byref(data_type), data, ctypes.byref(data_len))
                    
                return data.value
            
            RegCloseKey = ctypes.windll.advapi32.RegCloseKey
            
        except __HOLE__:
            # Print a messaged suggesting they install these?
            #
            pass

        if RegOpenKeyEx is not None:
            
            # Get the GraphViz install path from the registry
            #
            hkey = None
            potentialKeys = [
                "SOFTWARE\\ATT\\Graphviz",
                "SOFTWARE\\AT&T Research Labs\\Graphviz",
            ]
            for potentialKey in potentialKeys:
                
                try:
                    hkey = RegOpenKeyEx( HKEY_LOCAL_MACHINE,
                        potentialKey, 0, KEY_QUERY_VALUE )
                    
                    if hkey is not None:
                        path = RegQueryValueEx( hkey, "InstallPath" )
                        RegCloseKey( hkey )
                        
                        # The regitry variable might exist, left by old installations
                        # but with no value, in those cases we keep searching...
                        if not path:
                            continue
                        
                        # 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 Exception, excp:
                    #raise excp
                    pass
                else:
                    break
                    


    # 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...
            path = r"C:\Program Files\att\Graphviz\bin"
            
        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/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
dataset/ETHPy150Open erocarrera/pydot/pydot.py/find_graphviz