1.判断是否迭代,reversed()内置函数的了解
# iterable: 可迭代的; 可以for循环
from collections import Iterable
# isinstance(1, int)
print(isinstance(1,Iterable))
print(isinstance({1,2,3},Iterable))
#reversed()函数是返回序列seq的反向访问的迭代子。参数可以是列表,元组,字符串,不改变原对象
print( [i for i in reversed([1,2,3,4])])
2.列表声称式
import random
li = []
for i in range(10):
li.append(random.randint(1,10))
# 普通的列表生成式;
print([random.randint(1,10) for i in range(10)])
print([i*i for i in range(1,8)])
[4, 4, 1, 6, 1, 4, 2, 3, 10, 2]
[1, 4, 9, 16, 25, 36, 49]
# 升级版本
# 1. 找出1~10之间所有的偶数;
# print([i for i in range(1,11) if i%2==0])
#
[2, 4, 6, 8, 10]
# 2.for嵌套for循环;
# 'ABC', '123'
print([i+j for i in 'ABC' for j in '123'])
['A1', 'A2', 'A3', 'B1', 'B2', 'B3', 'C1', 'C2', 'C3']
3.字典生成式
# 1. : 将所有的key值变为大写;
d = dict(a=1,b=2)
# 1-1. 传统方法:
new_d = {}
for i in d: # 'a' 'b'
new_d[i.upper()] = d[i]
print("key转化为大写的字典:", new_d)
# 1-2. 升级
print({k.upper():v for k,v in d.items()})
key转化为大写的字典: {‘A’: 1, ‘B’: 2}
{‘A’: 1, ‘B’: 2}
# # 2:大小写key值合并, 统一以小写key值输出;
d = dict(a=2, b=1, c=2, B=9, A=5)
## 2-2. 字典生成式:
print({k.lower():d.get(k.lower(),0)+d.get(k.upper(),0) for k in d})
#2-1. 传统方法:
# {'a':2, 'b':1, 'c':2}
new_d = {}
for k, v in d.items():
low_k = k.lower()
if low_k not in new_d:
new_d[low_k] = v
else:
new_d[low_k] += v
print(new_d)
{‘a’: 7, ‘b’: 10, ‘c’: 2}
{‘a’: 7, ‘b’: 10, ‘c’: 2}
3.集合生成式
print({i ** 2 for i in {1, 2, 3}})
print({i ** 2 for i in {1, 2, 3, 9, 12} if i % 3 == 0})
{1, 4, 9}
{81, 9, 144}