Python快速入门（3）列表、练习题

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 list
list.append('a')   ## Use append() to add elements
list.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