使用没有前导或尾随零的 f 字符串将数字转换为字符串？

Question

Update: as up to now (2019-09), masking leading or trailing zeros in decimal numbers formatted to string seems to be unsupported in Python. You will need to use a workaround to get something like '.01' from the number 0.0101 (assuming 3 decimal places desired).

I would even argue that it's a good thing not to support such a format since

I'd consider '0.01' be better in terms of readability than '.01'

'0.010' carries information (3 digits of precision...) that is lost in '0.01'

If desired anyway, one could use one of the suggestions below. Thank you all for contributing.

问：我正在寻找一种将浮点数输出为字符串的方法，格式为 without leading/trailing zeros .有没有办法用 '{ }'.format() 或 f-string 来做到这一点？我搜索了互联网，但没有找到任何东西。我只是错过了还是不可能 (Python 3.7)？我的想法基本上是

some_number = 0.3140
string = f'{some_number:x}' # giving '.314'

给出输出 string '.314'.。那么有没有 x 可以做到这一点？

当然可以使用 lstrip / rstrip 来变通，例如here or similar here:

In [93]: str(0.3140).lstrip('0').rstrip('0')
Out[93]: '.314'

但是只使用一个f-string会更方便。由于我可以将其用于其他格式设置选项，因此可选地调用 strip 需要额外的代码行。

Answer 1

如果你只想从浮点数中去掉 0，你可以使用这个 "hack"

"." + str(0.314).split("0.")[-1]

这绝不是一个优雅的解决方案，但它可以完成工作

此外，如果您也想使用 .format，则不需要另一行，您可以

"." +str(0.314).split("0.")[-1].format('')

Answer 2

如果您想使用format()，请尝试以下操作。

print("Hello {0}, your balance is {1}.".format("Adam", "0.314".lstrip('0')))

只需在格式化函数中使用lstrip()，您无需编写额外的代码行。

Answer 3

这是我想出的一个辅助函数，因为无法避免 strip 解决方法：

def dec2string_stripped(num, dec_places=3, strip='right'):
    """
    Parameters
    ----------
    num : float or list of float
        scalar or list of decimal numbers.
    dec_places : int, optional
        number of decimal places to return. defaults to 3.
    strip : string, optional
        what to strip. 'right' (default), 'left' or 'both'.

    Returns
    -------
    list of string.
        numbers formatted as strings according to specification (see kwargs).
    """
    if not isinstance(num, list): # might be scalar or numpy array
        try:
            num = list(num)
        except TypeError: # input was scalar
            num = [num]

    if not isinstance(dec_places, int) or int(dec_places) < 1:
        raise ValueError(f"kwarg dec_places must be integer > 1 (got {dec_places})")

    if strip == 'right':
        return [f"{n:.{str(dec_places)}f}".rstrip('0') for n in num]
    if strip == 'left':
        return [f"{n:.{str(dec_places)}f}".lstrip('0') for n in num]
    if strip == 'both':
        return [f"{n:.{str(dec_places)}f}".strip('0') for n in num]
    raise ValueError(f"kwarg 'strip' must be 'right', 'left' or 'both' (got '{strip}')")

Answer 4

只是在这里提一下...如果您使用 numpy 还有函数 np.format_float_positional() 可以让您完全控制如何将数字显示为字符串和 trim 尾随零...

来自 np.format_float_positional 的文档：

Format a floating-point scalar as a decimal string in positional notation.

Provides control over rounding, trimming and padding. Uses and assumes IEEE >unbiased rounding. Uses the "Dragon4" algorithm.

去掉前导零只是一个简单的检查我们是否正在处理一个以 0 开头的数字

import numpy as np
def format_float(x, trim_leading=True, **kwargs):
    s = np.format_float_positional(x, **kwargs)
    if trim_leading is True and int(x) == 0 and len(s) > 1:
        s = s.replace("0.", ".")
    return s

format_float(0.0234001232, trim_leading=True, precision=4)
>>> '.0234'
format_float(0.0234001232, trim_leading=False, precision=4)
>>> '0.0234'
format_float(0.0234001232, precision=8)
>>> '0.02340012'
format_float(12.000558, precision=2, trim="-", fractional=False)
>>> '12'

使用没有前导或尾随零的 f 字符串将数字转换为字符串？

Number to string conversion with f-string without leading or trailing zeros?

python

string

format

f-string