Python快速入门（3）列表、练习题

06

序列：（三种类型）
字符串   不可以修改
列表list []  可以修改   ex.[1,2.3]
元组tuple ()  不可以修改  ex. uinfo = ('well,'male',20,'njupt')

----特点：
1.可以进行索引，索引为负数，则从右边开始计数
2.可以使用切片操作符 [m:n]

----基本序列操作：
1. len()
2. +  #拼接
3. *n #重复n次
4. in #判断元素是否在序列中
5. max()  #返回最大的值
6. min()  #返回最小的值
7. cmp(seq1,seq2)   #比较2个序列值是否相同


07
列表list：[]  ---- 可变的！

namelist = ['well','tom']nl = namelist  ##does not copy the list#Instead, assignment makes the two variables point to the one list in memory.

----专属操作：
1. list.append  #追加一个值 namelist.append('lucy')

2. del   #del namelist[1] 删除列表索引为1的元素
3. list.remove  #删除第一个匹配性 namelist.remove('well')

-------
tuple(seq)  #将序列转换为tuple
list(seq)   #将列表转换为list

创建列表：

list = []          ## Start as the empty listlist.append('a')   ## Use append() to add elementslist.append('b')

 
列表切片：同字符串切片一样

list = ['a', 'b', 'c', 'd']print list[1:-1]   ## ['b', 'c']list[0:2] = 'z'    ## replace ['a', 'b'] with ['z']print list         ## ['z', 'c', 'd']

for 和 in ：

for var in list  #遍历一个列表value in collection #测试集合中是否存在一个值

Range:
#The range(n) function yields the numbers 0, 1, ... n-1, 
#and range(a, b) returns a, a+1, ... b-1 -- up to but not including the last number. 

while循环：

List常用方法：

list.append(elem) #-- adds a single element to the end of the list. Common error: does not return the new list, just modifies the original.list.insert(index, elem) #-- inserts the element at the given index, shifting elements to the right.list.extend(list2) #adds the elements in list2 to the end of the list. Using + or += on a list is similar to using extend().list.index(elem) -- #searches for the given element from the start of the list and returns its index. Throws a ValueError if the element does not appear (use "in" to check without a ValueError).list.remove(elem) -- #searches for the first instance of the given element and removes it (throws ValueError if not present)list.sort() -- #sorts the list in place (does not return it). (The sorted() function shown below is preferred.)list.reverse() -- #reverses the list in place (does not return it)list.pop(index) -- #removes and returns the element at the given index. Returns the rightmost element if index is omitted (roughly the opposite of append()).

      相关练习：

# C. sort_last
# Given a list of non-empty tuples, return a list sorted in increasing
# order by the last element in each tuple.
# e.g. [(1, 7), (1, 3), (3, 4, 5), (2, 2)] yields
# [(2, 2), (1, 3), (3, 4, 5), (1, 7)]
# Hint: use a custom key= function to extract the last element form each tuple.

def last(a):  return a[-1]def sort_last(tuples):  # +++your code here+++  return sorted(tuples,key=last)

# E. Given two lists sorted in increasing order, create and return a merged
# list of all the elements in sorted order. You may modify the passed in lists.
# Ideally, the solution should work in "linear" time, making a single
# pass of both lists.

def linear_merge(list1, list2):  # +++your code here+++  # LAB(begin solution)  result = []  # Look at the two lists so long as both are non-empty.  # Take whichever element [0] is smaller.  while len(list1) and len(list2):if list1[0] < list2[0]:  result.append(list1.pop(0))else:  result.append(list2.pop(0))  # Now tack on what's left  result.extend(list1)  result.extend(list2)  return result