【Python for Everybody】10 Turple

Turples and Lists

Turples are like lists

but tueples are immutable

可以将turple理解成limited list
因为turple不可修改，它比list效率更高、占用内存更小
对于temporary variable，一般我们使用turple而非list

method

只有两个
count()某个元素在元组中出现的次数
index()返回索引，和list相同

Turples and Assignment

turple的一个赋值语句可以给两个变量赋值
左边的括号可以省略

Turples and Dictionaries

Turples and Comparable

comparison operator适用于turple，从左至右依次进行比较，第一个元素如果能比出结果就不会再继续读取元素比较
only scans until it has a definite answer, it won’t scan any further

Sorting list of turples

sorted()

sort by value instead of key

用for循环将key-value pair变成value-key pair

计算文档中词频前十的词例子

fhand = open 'wordcount.txt'
counts = dict()
for line in fhand:
	words = line.split()
	for word in words:
		 counts[word] = counts.get(word, 0) + 1

list = list()
for key, value in counts.item():
	newpair = (value, key)  
	list.append(newpair)  # append里也是新turple

list = sorted(list, reverse = True)

for value, key in list[: 10]:
	print(key, value)  # print的时候key在前更符合习惯

List Comprehension

列表推导式

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