Python内置函数(6)—

英文文档：

round(number[, ndigits])


Return the floating point value number rounded to ndigits digits after the decimal point. If ndigits is omitted, it returns the nearest integer to its input. Delegates to number.__round__(ndigits).


For the built-in types supporting round(), values are rounded to the closest multiple of 10 to the power minus ndigits; if two multiples are equally close, rounding is done toward the even choice (so, for example, both round(0.5) and round(-0.5) are 0, and round(1.5) is 2). The return value is an integer if called with one argument, otherwise of the same type as number.


Note：

The behavior of round() for floats can be surprising: for example, round(2.675, 2) gives 2.67 instead of the expected 2.68. This is not a bug: it’s a result of the fact that most decimal fractions can’t be represented exactly as a float. See Floating Point Arithmetic: Issues and Limitations for more information.

说明：

1.round 函数用于对浮点数进行四舍五入的求值，具体保留几位小数，以出阿如的 ndigits 参数来控制

>>> round(1.423432432)

1

>>>

>>> round(1.423432432,2)

1.42

>>> round(1.423432432,5)

1.42343

>>>

>>>

>>> round(1.423432432)

1

>>>

　　2. ndigits参数为可选参数，当不传入时，即以默认保留0位小数进行取整，返回的是整数。

>>> round(1.1314926)

1

　3.当传入的值是0时与不传值一样保留0位小数，但是是浮点类型的数

>>> round(1.423432432,0)

1.0

>>>

　　4.也可以传入负数，则标示是对整数部分进行四舍五入，小数部分全部清0，若果传入的 ndigits 值大于浮点数的整数部分，则返回0.0

>>> round(1314.423432432,-2)

1300.0

>>> round(1314.423432432,-4)

0.0

>>>

　　5.round 四舍五入是靠近0原则，所以-0.5和0.5进行0位的四舍五入结果都是0，

>>> round(0.5)

0

>>> round(-0.5)

0

>>>

　　6.round 有时会有 bug，因为浮点数在存储的时候因为数位有限，存储的不精却，存储的值和实际显示的值有误差，导致四舍五入的时候也不精确。

>>> round(2.2458,3)

2.246

>>> round(2.245,3)

2.245

>>> round(2.245,2)

2.25

>>> round(2.675,2)

2.67

>>> round(2.674545,4)

2.6745

>>>

>>>

　　7.round 对整数也能进行操作，但会也是整形。

>>>

>>> round(123)

123

>>> round(123,2)

123

>>> round(123,-2)

100

>>> round(123,-3)

0

>>>

巴特西

Python内置函数(6)——round

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