python - 以指定精度舍入和修整数字

Question

假设我有一个函数，它接受一个 float 并返回一个转换为具有 2 位预定义精度的字符串:

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

它的工作原理如下:

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

我怎样才能让这个函数接受一个名为 precision 的参数，这样它就不会转换为硬编码的精度值 2，而是使用 precision 中的值？

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

您可以嵌套替换字段，例如:

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

因此，当 precision 为 3 时，格式字符串实际上将变为 "{0:.3f}"。

来自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.