具有指定精度的舍入和修剪数字

Question

假设我有一个函数，它接受float并返回到字符串的转换，其预定义精度为2位：

def round_and_trim(x):
    return "{0:.2f}".format(round(x,2))

其工作原理如下：

x = 0.238498
y = round_and_trim(x)
y = "0.24"

我怎样才能使这个函数接受一个名为precision的参数，这样它就不用转换成硬编码的精度值2，而是使用precision中的值？你知道吗

例如

x = 0.238498
y = round_and_trim(x, precision=4)
y = "0.2385"

或：

x = 0.238498
y = round_and_trim(x, precision=3)
y = "0.238"

Answer 1

可以嵌套替换字段，例如：

def round_and_trim(x, precision=2):
    return "{0:.{prec}f}".format(round(x, precision), prec=precision)

因此，当precision是3时，格式字符串实际上将变成"{0:.3f}"。你知道吗

从docs：

A *format_spec* field can also include nested replacement fields within it. These nested replacement fields can contain only a field name; conversion flags and format specifications are not allowed. The replacement fields within the *format_spec* are substituted before the *format_spec* string is interpreted. This allows the formatting of a value to be dynamically specified.