各种推导式

 

# 列表推导式___________________________________

# 30以内所有能被3整除的数的平方
num = [i * i for i in range(1, 31) if i%3 == 0]
print(num)

# 找到嵌套列表中含有两个'e'的所有名字
names = [['Tom', 'Billy', 'Jefferson', 'Andrew', 'Wesley', 'Steven', 'Joe'],
         ['Alice', 'Jill', 'Ana', 'Wendy', 'Jennifer', 'Sherry', 'Eva']]
print([name for lst in names for name in lst if name.count('e') >= 2])  # 注意遍历顺序，这是实现的关键


# 字典推导式___________________________________

# 将字典的key和value调换
mcase = {'a': 10, 'b': 34}
mcase_frequency = {mcase[k]: k for k in mcase}
print(mcase_frequency)

# 合并大小写对应的value值，将k统一成小写
mcase = {'a': 10, 'b': 34, 'A': 7, 'Z': 3}
mcase_frequency = {k.lower(): mcase.get(k.lower(), 0) + mcase.get(k.upper(), 0) for k in mcase.keys()}
print(mcase_frequency)


# 集合推导式___________________________________
# 计算列表中每个值的平方，自带去重功能
squared = {x**2 for x in [1, -1, 2]}
print(squared)
# Output: set([1, 4])