“`pint`”中导出尺寸数量的标准格式

Question

TLDR: I希望在一个特定(派生)维度中的pint数量在默认情况下转换为一个预先设置的单元。

详细信息：

我处理5个维度，如下所述。注意，电源和价格是派生的维度。

# units.txt

# Base dimensions and their units
hour = [time] = h = hr
megawatthour = [energy] = MWh
euro = [currency] = Eur = €

# Derived dimensions and their units
[power] = [energy] / [time]
megawatt = megawatthour / hour = MW
[price] = [currency] / [energy]
euro_per_MWh = euro / megawatthour  = Eur/MWh

我的问题是:是否可以指定具有尺寸功率的计算量在默认情况下转换为兆瓦？

下面是一个例子：

import pint

ureg = pint.UnitRegistry("units.txt",)
ureg.default_format = ".0f~P"

energy = 100 * ureg.MWh
time = 4 * ureg.h
revenue = 4000 * ureg.euro

price = revenue / energy
power = energy / time

print(energy, time, revenue, price, power) 
# 100 MWh 4 h 4000 Eur 40 Eur/MWh 25 MWh/h

在这里，功率是以MWh/h表示的，因为它的计算方式，我可以通过调用power.to('MW')将其“转换”为MW。是否可以在每次计算此维度中的数量时自动完成此操作？

请注意，对所有数量做一个毯子.to_base_units()会将其恢复到MWh/h。

备注：

• 我不想把权力作为基本维度。不管怎样，这就把问题推到了价格上。
• 我知道前缀；我只是把它们放在这里，以使示例尽可能简短。

Answer 1

据我所知，Pint目前不支持设置所需的转换首选项。在项目回购和这个问题链接到一系列相关的问题上，有一些关于这个问题的讨论。

您想要的东西可以通过一些自定义代码来实现，但是需要在函数中包装输出。

# units-2.txt

# Base dimensions and their units
hour = [time] = h = hr
megawatt = [power] = MW 
euro = [currency] = Eur = €

# Derived dimensions and their units
[energy] = [power] * [time]
megawatthour = megawatt * hour = MWh
[price] = [currency] / [energy]
euro_per_MWh = euro / megawatthour  = Eur/MWh

import pint

preference = ["Eur/MWh", 'MW']

def beautify(x, preference=preference):
    for preferred_unit in preference:
        try:
            return x.to(preferred_unit)
        except pint.DimensionalityError:
            pass
    # if no preferred unit fits, leave it as it is
    return x

def test_defs(file):
    print(file)
    ureg = pint.UnitRegistry(file,)
    ureg.default_format = ".0f~P"
    energy = 100 * ureg.MWh
    time = 4 * ureg.h
    revenue = 4000 * ureg.euro
    price = revenue / energy
    power = energy / time
    print(time.to_base_units())
    print(f"beautified time: {beautify(time)}")  # Units with no preference remain the same.
    print(power.to_base_units())
    print(f"beautified power: {beautify(power)}")  # Units with preference can be changed.
    print(price.to_base_units())
    print(f"beautified price: {beautify(price)}")  # Units with preference can be changed.

test_defs("units.txt")
test_defs("units-2.txt")

这个会打印出来

units.txt
4 h
beautified time: 4 h
25 MWh/h
beautified power: 25 MW
40 Eur/MWh
beautified price: 40 Eur/MWh
units-2.txt
4 h
beautified time: 4 h
25 MW
beautified power: 25 MW
40 Eur/MW/h
beautified price: 40 Eur/MWh