这节复习函数的定义和调用，以及模块导入
详细内容见笨办法笔记17
教材代码
#ex25.py
def break_words(stuff):
words = stuff.split(',')
return words
def sort_words(words):
return sorted(words)
def print_first_word(words):
word = words.pop(0)
return word
def print_last_word(words):
word = words.pop(-1)
print word
def sort_sentence(sentence):
words = break_words(sentence)
return sort_words(words)
def print_first_and_last(sentence):
words = break_words(sentence)
print_first_word(words)
print_last_word(words)
def print_first_and_last_sorted(sentence):
words = sort_sentence(sentence)
print_first_word(words)
print_last_word(words)
1.函数的定义
以关键字def开始
函数名能体现出函数的功能
括号中可使用参数，括号后面紧跟冒号
函数体以相同缩进为标志
2.函数的调用
函数需先定义才可对其进行调用
3.模块的导入
将ex25.py导入到另一个脚本中，以便能使用ex25.py中定义的函数。
import ex25
或者
from ex25 import *
4.代码中涉及到几个新的函数
split
str.split([sep[, maxsplit]])
Return a list of the words in the string, using sep as the delimiter string. If maxsplit is given, at most maxsplit splits are done (thus, the list will have at most maxsplit+1 elements). If maxsplit is not specified or -1, then there is no limit on the number of splits (all possible splits are made).
If sep is given, consecutive delimiters are not grouped together and are deemed to delimit empty strings (for example, '1,,2'.split(',') returns ['1', '', '2']). The sep argument may consist of multiple characters (for example, '1<>2<>3'.split('<>') returns ['1', '2', '3']). Splitting an empty string with a specified separator returns [''].
If sep is not specified or is None, a different splitting algorithm is applied: runs of consecutive whitespace are regarded as a single separator, and the result will contain no empty strings at the start or end if the string has leading or trailing whitespace. Consequently, splitting an empty string or a string consisting of just whitespace with a None separator returns [].
For example, ' 1 2 3 '.split() returns ['1', '2', '3'], and ' 1 2 3 '.split(None, 1) returns ['1', '2 3 '].
split()函数根据分隔符对字符串进行分隔成段。返回一个列表。
参数中可设置分隔符和最大分隔次数
sorted
sorted(iterable[, cmp[, key[, reverse]]])
Return a new sorted list from the items in iterable.
The optional arguments cmp, key, and reverse have the same meaning as those for the list.sort() method (described in section Mutable Sequence Types).
cmp specifies a custom comparison function of two arguments (iterable elements) which should return a negative, zero or positive number depending on whether the first argument is considered smaller than, equal to, or larger than the second argument: cmp=lambda x,y: cmp(x.lower(), y.lower()). The default value is None.
key specifies a function of one argument that is used to extract a comparison key from each list element: key=str.lower. The default value is None (compare the elements directly).
reverse is a boolean value. If set to True, then the list elements are sorted as if each comparison were reversed.
In general, the key and reverse conversion processes are much faster than specifying an equivalent cmp function. This is because cmp is called multiple times for each list element while key and reverse touch each element only once. Use functools.cmp_to_key() to convert an old-style cmp function to a key function.
The built-in sorted() function is guaranteed to be stable. A sort is stable if it guarantees not to change the relative order of elements that compare equal — this is helpful for sorting in multiple passes (for example, sort by department, then by salary grade).
sorted()对对象进行排序，最后一个参数可用于设置升序或降序排列
pop
pop(...)
L.pop([index]) -> item -- remove and return item at index (default last).
Raises IndexError if list is empty or index is out of range.
pop() 函数用于移除列表中的一个元素（默认最后一个元素），并且返回该元素的值。
如果列表为空或者索引超出范围，会引发一个IndexError异常。
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