Python3学习笔记

补充上面关于 cmp() 函数的问题，官方文档中有如下描述： (If you really need the cmp() functionality, you could use the expression (a > b) - (a < b) as the equivalent for cmp(a,b).)

补充上面关于round()函数的问题，注意下面例子：

>>> round(1.05,1)

1.1

>>> round(1.15,1)

1.1

>>> round(1.55,1)

1.6

>>> round(2.05,1)

2.0

>>> round(2.15,1)

2.1

>>> round(2.55,1)

2.5

官方的解释是：这不是bug，而事关浮点数存储：

>>>fromdecimalimportDecimal

>>>Decimal.from_float(1.05)

Decimal('1.0500000000000000444089209850062616169452667236328125')

>>>Decimal.from_float(1.15)

Decimal('1.149999999999999911182158029987476766109466552734375')

>>>Decimal.from_float(1.55)

Decimal('1.5500000000000000444089209850062616169452667236328125')

>>>Decimal.from_float(2.05)

Decimal('2.04999999999999982236431605997495353221893310546875')

>>>Decimal.from_float(2.15)

Decimal('2.149999999999999911182158029987476766109466552734375')

>>>Decimal.from_float(2.55)

Decimal('2.54999999999999982236431605997495353221893310546875')

尽量避免使用round()。