在这一章的学习中，做了一些函数和变量的练习。并不是直接运行脚本，而是在脚本中定义了一些函数，把他们导入到Python中通过执行函数的方式运行。先看代码：

def break_words(stuff):    """This function will break up words for us."""    words = stuff.split(' ')    return wordsdef sort_words(words):    """Sorts the words."""    return sorted(words)def print_first_word(words):    """Prints the first word after popping it off."""    word = words.pop(0)    print worddef print_last_word(words):    """Prints the last word after popping it off."""    word = words.pop(-1)    print worddef sort_sentence(sentence):    """Takes in a full sentence and returns the sorted words."""    words = break_words(sentence)    return sort_words(words)def print_first_and_last(sentence):    """Prints the first and last words of the sentence."""    words = break_words(sentence)    print_first_word(words)    print_last_word(words)def print_first_and_last_sorted(sentence):    """Sorts the words then prints the first and last one."""    words = sort_sentence(sentence)    print_first_word(words)    print_last_word(words)

可以看到这个程序中只定义了函数，并没有调用函数并打印出来。我们需要使用import的方法把整个程序导入到python中，然后直接在python中使用程序中的各种功能。

导入函数的方法有两种：import no25 或 from no25 import * (我写的脚本名称叫no25.py）下面是执行结果：

-userdeMacBook-Air:desktop user$ pythonPython 2.7.11 (v2.7.11:6d1b6a68f775, Dec  5 2015, 12:54:16) [GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwinType "help", "copyright", "credits" or "license" for more information.>>> import no25>>> sentence = "I am the king of the world!">>> word = no25.break_words(sentence)>>> word['I', 'am', 'the', 'king', 'of', 'the', 'world!']>>> sorted_word = no25.sort_words(word)>>> sorted_word['I', 'am', 'king', 'of', 'the', 'the', 'world!']>>> no25.print_first_word(word)I>>> no25.print_last_word(word)world!['am', 'the', 'king', 'of', 'the']>>> no25.print_first_word(word)am>>> no25.print_last_word(word)the>>> sorted_sentence = no25.sort_sentence(sentence)>>> sorted_sentence['I', 'am', 'king', 'of', 'the', 'the', 'world!']>>> no25.print_first_and_last(sentence)Iworld!>>> no25.print_first_and_last_sorted(sentence)Iworld!>>>

-userdeMacBook-Air:Desktop user$ pythonPython 2.7.11 (v2.7.11:6d1b6a68f775, Dec  5 2015, 12:54:16) [GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwinType "help", "copyright", "credits" or "license" for more information.>>> from no25 import *>>> sentence = "All things was very good!">>> short = break_words(sentence)>>> short['All', 'things', 'was', 'very', 'good!']>>> sort_words(short)['All', 'good!', 'things', 'very', 'was']>>> print_first_word(short)All>>> print_last_word(short)good!>>> sorted_sentence = sort_sentence(sentence)>>> short['things', 'was', 'very']>>> sorted_words = sort_sentence(sentence)>>> sorted_words['All', 'good!', 'things', 'very', 'was']>>> print_first_and_last(sentence)Allgood!>>> print_first_and_last_sorted(sentence)Allwas>>>

下面是在Python中执行时遇到的一些错误：

错误1：split方法中引号里没有添加空格。

'split'方法中必须指定一个分隔符，如果引号中没有任何内容，就会提示“语法错误”，"ValueError: empty separator"。正确用法：使用split(' ')，分隔符，默认为所有的空字符，包括空格、换行(\n)、制表符(\t)等。

Bing到这个网页，在StackOverflow上有人有同样的问题。

可惜我的网络一直打不开网页，只能通过Bing的Cache来访问，555……

Eldad AK这位老兄解释的很清楚

具体错误提示如下：

-userdeMacBook-Air:desktop user$ pythonPython 2.7.11 (v2.7.11:6d1b6a68f775, Dec  5 2015, 12:54:16) [GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwinType "help", "copyright", "credits" or "license" for more information.>>> import os>>> import sys>>> import no25>>> s = "There are many books.">>> sen = no25.break_words(s)Traceback (most recent call last):  File "
    
     ", line 1, in 
     
        File "no25.py", line 4, in break_words    words = stuff.split('') ValueError: empty separator
     
    

错误2：调用函数打错字导致python提示名称未定义。

我在程序中第46行下面调用了一个函数print_first_words()，但是在程序里并没有定义这个函数，而是有print_first_word()这个函数，所以是手误打错了，python的错误提示"NameError: …… is not defined"，可以帮助我们快速定位问题。

>>> no25.print_first_and_last(sentence)Traceback (most recent call last): File "
    
     ", line 1, in 
     
       File "no25.py", line 46, in print_first_and_last   print_first_words(words)NameError: global name 'print_first_words' is not defined
     
    

错误3：当前目录没有no25.py脚本，我的脚本放在Desktop下，而新开的mac Command Line的目录为当前用户的Home目录。

可以看到python提示"No module named no25"，说明python在库中找不到叫no25的模块，仔细观察一下，发现我使用的是相对路径，当前目录是～，也就是user用户的家目录，所以找不到。

-userdeMacBook-Air:~ user$ pythonPython 2.7.11 (v2.7.11:6d1b6a68f775, Dec  5 2015, 12:54:16) [GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwinType "help", "copyright", "credits" or "license" for more information.>>> from no25 import *Traceback (most recent call last):  File "
    
     ", line 1, in 
     
      ImportError: No module named no25>>> import no25Traceback (most recent call last):  File "
      
       ", line 1, in 
       
        ImportError: No module named no25