lambda表達式常常用來聲明匿名函數。lambda表達式只可包含一個表達式，但在表達式中可以調用其他函數，該表達式的計算結果相當於函數的返回值。下面代碼演示lambda表達式的應用。
f = lambda x, y, z: x+y+z
print(f(1,2,3))
# 6
g = lambda x, y=2, z=3: x+y+z
print(g(1))
# 6
print(g(2, z=4, y=5))
# 11
L = [(lambda x: x**2),(lambda x: x**3),(lambda x: x**4)]
print(L[0](2), L[1](2), L[2](2))
# 4 8 16
D = {'f1':(lambda: 2+3), 'f2':(lambda:2*3), 'f3':(lambda:2**3)}
print(D['f1'](), D['f2'](), D['f3']())
# 5 6 8
L = [1, 2, 3, 4, 5]
print(map((lambda x: x+10), L)) #沒有名字的lambda表達式，作爲函數參數
# [11, 12, 13, 14, 15]
L
# [1, 2, 3, 4, 5]
在lambda表達式中調用函數：
>>>def demo(n):
>>>return n * n
>>>demo(5)
25
>>>a_list = [1, 2, 3, 4, 5]
>>>map(lambda x: demo(x), a_list) #在lambda表達式中調用函數
[1, 4, 9, 16, 25]
>>>data = list(range(20))
>>>print(data)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]
>>>import random
>>>random.shuffle(data)
>>>data
[19, 4, 18, 12, 5, 15, 0, 17, 7, 13, 2, 10, 8, 6, 3, 9, 1, 16, 11, 14]
>>>data.sort(key=lambda x: x) #用在列表的sort()方法中，作爲函數參數
>>>data
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]
>>>data.sort(key=lambda x: len(str(x))) #使用lambda指定排序規則
>>>data
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]
>>>data.sort(key=lambda x: len(str(x)), reverse=True)
>>>data
[10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9]