上一篇《Python笔记：string, tuple，list，dictionary的区别(之一，基本用法与区别)》讲述了这四种类型的基本用法与区别，本篇讲述的是高级用法与类型转换。
tuple的用法
平时写代码tuple用的不多。具体的用法在MIT的python课程里提到过两种。
1. 定义函数的返回值时，用tuple可以返回多个值。但是我发现list也有这个功能，可能tuple的不可修改性更适合完成这个场景。
#used to return more than one value from a function
def quotient_and_remainder(x, y):
q = x // y
r = x % y
return(q, r)
result = quotient_and_remainder(4,5)
print(result)(0, 4)
2.互换赋值(swap)，python的这种操作可以减少一个临时变量的使用。这种用法同样可以用在list类型上。
x_tuple = ('a',1)
y_tuple = ('b',2)
(x_tuple, y_tuple) = (y_tuple, x_tuple)
print(x_tuple)
print(y_tuple)('b', 2)
('a', 1)
list 的用法
list作为一种常见object，有很多的method可以用。
x_list = ['Peggy','Susie','Daniel']
y_list = ['Pedro','Rebecca']
print(x_list)
print(y_list)['Peggy', 'Susie', 'Daniel']
['Pedro', 'Rebecca']
| Expression | Result |
|---|---|
| x_list.append(‘George’) | x_list = [‘Peggy’, ‘Susie’, ‘Daniel’, ‘George’] |
| x_list.pop() | x_list = [‘Peggy’, ‘Susie’, ‘Daniel’] |
| x_list.extend(y_list) | x_list = [‘Peggy’, ‘Susie’, ‘Daniel’, ‘Pedro’, ‘Rebecca’] |
| x_list.remove(‘Daniel’) | x_list = [‘Peggy’, ‘Susie’, ‘Pedro’, ‘Rebecca’] |
| del(x_list[1]) | x_list = [‘Peggy’, ‘Pedro’, ‘Rebecca’] |
x_list.append('George')
print(x_list)
x_list.pop()
print(x_list)
x_list.extend(y_list)
print(x_list)
x_list.remove('Daniel')
print(x_list)
del(x_list[1])
print(x_list)['Peggy', 'Susie', 'Daniel', 'George']
['Peggy', 'Susie', 'Daniel']
['Peggy', 'Susie', 'Daniel', 'Pedro', 'Rebecca']
['Peggy', 'Susie', 'Pedro', 'Rebecca']
['Peggy', 'Pedro', 'Rebecca']
string 和list 之间的转换，split()，join() 用于文本分析
- string可以使用split()函数，将其中每一个单词分离成单独元素，结果是list类型。
text_string = 'Who knows what will happen in the future?'
text_string.split()[-1]'future?'
text_list = text_string.split()
text_list['Who', 'knows', 'what', 'will', 'happen', 'in', 'the', 'future?']
2. list可以使用join()函数，将很多个字符串用指定的符号链接起来，返回字符串类型
text_string_rejoin = ' '.join(text_list)
text_string_rejoin'Who knows what will happen in the future?'
生成dictionary的方法
- 通过字符串生成字典，在文本处理中常见。
data = 'the quick brown fox jumps over a lazy dog.'
chars = list(set(data))
data_size, vocab_size = len(data), len(chars)
print('There are %d total characters and %d unique characters in your data.' % (data_size, vocab_size))There are 42 total characters and 28 unique characters in your data.
char_to_ix = { ch:i for i,ch in enumerate(sorted(chars)) }
ix_to_char = { i:ch for i,ch in enumerate(sorted(chars)) }
print(ix_to_char)
print(char_to_ix){0: ' ', 1: '.', 2: 'a', 3: 'b', 4: 'c', 5: 'd', 6: 'e', 7: 'f', 8: 'g', 9: 'h', 10: 'i', 11: 'j', 12: 'k', 13: 'l', 14: 'm', 15: 'n', 16: 'o', 17: 'p', 18: 'q', 19: 'r', 20: 's', 21: 't', 22: 'u', 23: 'v', 24: 'w', 25: 'x', 26: 'y', 27: 'z'}
{' ': 0, '.': 1, 'a': 2, 'b': 3, 'c': 4, 'd': 5, 'e': 6, 'f': 7, 'g': 8, 'h': 9, 'i': 10, 'j': 11, 'k': 12, 'l': 13, 'm': 14, 'n': 15, 'o': 16, 'p': 17, 'q': 18, 'r': 19, 's': 20, 't': 21, 'u': 22, 'v': 23, 'w': 24, 'x': 25, 'y': 26, 'z': 27}
2. 通过两个同样长度的list来生成字典
names = ["Peggy", "Susie", "Daniel"]
animals = ["pig", "sheep", "dog"]最直接的想法是分别对names，和animals做遍历赋值
names_animals = {}
for i in range(len(names)):
names_animals[names[i]] = animals[i]
print(names_animals){'Peggy': 'pig', 'Susie': 'sheep', 'Daniel': 'dog'}
另一种方法，是调用zip函数将两个list合并，再做for循环。这种方法更像python的风格。
names_animals = {}
names_animals_zipped = zip(names, animals)
names_animals = { name:animal for name,animal in names_animals_zipped }
print(names_animals){'Peggy': 'pig', 'Susie': 'sheep', 'Daniel': 'dog'}