Python中lambda和in指用法小结

in的用法小结

枚举或遍历

>>> for i in range(100):
	print(i)	
0
1
2
3
4
5
6
7

判断

if 1 in aa:
print 'Very Good'
else:
print 'Not Bad'

筛选

if 'a' in 'dcv55a'
print 'ok'

字典中用法

my_dict = {i: i * i for i in range(100)}
>>> my_dict
{0: 0, 1: 1, 2: 4, 3: 9, 4: 16, 5: 25, 6: 36, 7: 49, 8: 64, 9: 81, 10: 100, 11: 121, 12: 144, 13: 169, 14: 196, 15: 225, 16: 256, 17: 289, 18: 324, 19: 361, 20: 400, 21: 441, 22: 484, 23: 529, 24: 576, 25: 625, 26: 676, 27: 729, 28: 784, 29: 841, 30: 900, 31: 961, 32: 1024, 33: 1089, 34: 1156, 35: 1225, 36: 1296, 37: 1369, 38: 1444, 39: 1521, 40: 1600, 41: 1681, 42: 1764, 43: 1849, 44: 1936, 45: 2025, 46: 2116, 47: 2209, 48: 2304, 49: 2401, 50: 2500, 51: 2601, 52: 2704, 53: 2809, 54: 2916, 55: 3025, 56: 3136, 57: 3249, 58: 3364, 59: 3481, 60: 3600, 61: 3721, 62: 3844, 63: 3969, 64: 4096, 65: 4225, 66: 4356, 67: 4489, 68: 4624, 69: 4761, 70: 4900, 71: 5041, 72: 5184, 73: 5329, 74: 5476, 75: 5625, 76: 5776, 77: 5929, 78: 6084, 79: 6241, 80: 6400, 81: 6561, 82: 6724, 83: 6889, 84: 7056, 85: 7225, 86: 7396, 87: 7569, 88: 7744, 89: 7921, 90: 8100, 91: 8281, 92: 8464, 93: 8649, 94: 8836, 95: 9025, 96: 9216, 97: 9409, 98: 9604, 99: 9801}

lambda表达式用法

单个参数的：
g = lambda x:x*2
print g(3)
结果是6

多个参数的：
m = lambda x,y,z: (x-y)*z
print m(3,1,2)

结果是4

map()的用法
map(function, sequence) ：对sequence中的item依次执行function(item)，见执行结果组成一个List返回：

a = [1, 2, 3]

f = lambda x : x + 1

map(f, a)

等价于map( lambda x : x + 1, [1, 2, 3] )

map类似于

a = [1, 2, 3]
r = []
for each in a:
    r.append(each+1)