笨方法学Python练习48：为什么我执行nosetests 命令之后，命令行卡住了？

Question

nosetests 命令卡死
笨方法学Python练习48：nosetests 命令卡死
(初次发帖，如果有什么做的不好的地方，还请指出。)

在笨方法学Python的ex48中，我编写的lexicon类使得测试命令nosetests卡死了。
而我自己将test中的每个函数在控制台人肉run过一遍，并没有出现卡死的情况。
I need help...

运行nosetests之后：

CTRL+C之后 ：

运行很久之后 CTRL+C ：

lexicon 代码如下：

class Lexicon( object ) :

def __init__( self ) :

    self.directions = [ 'north', 'south', 'east', 'west', 'down', 'up', 'left', 'right', 'back' ]
    self.verbs = [ 'go', 'stop', 'kill', 'eat' ]
    self.stops= [ 'the', 'in', 'of', 'form', 'at', 'it' ]
    self.nouns = [ 'door', 'bear', 'princess', 'cabinet' ]
    self.numbers = []


def lexicon( self ) :

    stuff = raw_input( "> " )
    words = stuff.split(" ")
    result = self.scan( words )        
    print result


def isNumber ( self, word ) :

    try :
        int( word )
        return True
    except ValueError :
        return False



def scan( self, words ) :

    result = []
    for word in words :
        if word in self.directions :
            result.append( ('direction', word) )
        elif word in self.verbs :
            result.append( ('verb', word) )
        elif word in self.verbs :
            result.append( ('stop', word ) )
        elif word in self.nouns :
            result.append( ('noun', word ) )
        elif word in self.stops :
            result.append( ('stop', word) )
        elif self.isNumber( word ) :
            result.append( ('number', int( word ) ) )
        else :
            result.append( ( 'error' , word ) ) 

    return result

单元测试代码如下 ：

from nose.tools import*
from ex48.ex48 import Lexicon

def test_directions() :
    assert_equal( Lexicon().scan("north"), [( 'direction', 'north' )] )
    result = Lexicon().scan( "north south east" )
    assert_equal( result, [ ('direction', 'north'),
                            ('direction', 'south'), 
                            ('direction', 'east') ] )

def test_verbs() :
    assert_equal( Lexicon().scan("go"), ['verb', 'go'] )
    result = Lexicon().scan( "go kill eat" )
    assert_equal( result, [ ('verb', 'go' ),
                            ('verb', 'kill'),
                            ('verb', 'eat') ] )

def test_stops() :
    assert_equal( Lexicon().scan("the"), [ ('stop', 'the') ] )
    result = Lexicon().scan( "the in of" )
    assert_equal( result, [ ('stop', 'the' ),
                            ('stop', 'in'),
                            ('stop', 'of') ] )

def test_nouns() :
    assert_equal( Lexicon().scan("bear"), [ ('noun', 'bear') ] )
    result = Lexicon().scan( "bear princess" )
    assert_equal ( result, [ ('noun', 'bear'),
                             ('noun', 'princess') ] )

def test_numbers() :
    assert_equal ( Lexicon().scan("1234"), [('number', 1234) ] )
    result = Lexicon().scan( "3 91234" )
    assert_equal( result, [('number', 3 ),
                           ('number', 91234 ) ] )

def test_errors() :
    assert_equal( Lexicon().scan("asdf"), [('error', 'asdf')] )
    result = Lexicon().scan( "bear IAS princess" )
    assert_equal( result, [('noun', 'bear'),
                           ('error', 'IAS'),
                           ('noun', 'princess') ] )

测试代码出处 ： http://www.kancloud.cn/kancloud/learn-python-hard-way/49926

实在是找不到解决方法了，特来求助。
不论如何，感谢浏览。

Answer 1

Ubuntu 14.04 亲测没有卡死，但是测试没有通过

Answer 2

from ex48.ex48 import Lexicon ==> from ex48 import Lexicon

Answer 3

运行 scan 的时候没有把 words 分解成word