Lambda表达式
“提示： 在python里面，如果一个函数只有一句话的话，可以用一种叫lambda表达式的东西代替。
- 示例一：
py
def power(x):
return x * x
print(power(5)) # 25上面的函数只有一个 return 语句，那么就可以用 lambda 表达式来简写
py
power = lambda x: x * x
print(power(5)) # 25- 示例二：
py
def sum(x, y):
return x + y
print(sum(3, 4)) # 7用 lambda 表达式简写
py
sum = lambda x, y: x + y
print(sum(3, 4)) #7- 示例三：
py
countries = []
file = open('./test.csv', 'r')
for line in file:
line = line.strip()
arr = line.split(',')
country_name = arr[1]
capital = arr[3]
population = int(arr[4])
countries.append((country_name, capital, population))
file.close()
def population_incre(country):
return country[2]
countries.sort(key = population_incre)
for country in countries:
print(country) #按人口总数升序排列
用 lambda 简写 sort 的 key ，省去了定义 population_incre 函数
py
countries = []
file = open('./test.csv', 'r')
for line in file:
line = line.strip()
arr = line.split(',')
country_name = arr[1]
capital = arr[3]
population = int(arr[4])
countries.append((country_name, capital, population))
countries.sort(key = lambda country: country[2])
for country in countries:
print(country) #按人口总数升序排列- 示例四：
py
def quadratic(a, b, c):
return lambda x: a * pow(x, 2) + b * x + c
f = quadratic(2, -1, 1) # f(x) = 2x² - x + 1
print(f(3)) #16
print(quadratic(2, -1, 1)(3)) #16