带有自定义占位符的高级 Python 字符串格式? [英] Advanced Python string formatting with custom placeholders?

问题描述

我在 Python 变量中有以下 HTML 模板:

I have the following HTML template in a Python variable:

template = """
    <script>
        function work()
        {
            alert('bla');
        }
    </script>

    Success rate is {value:.2%} percent.
"""

我想用一些具有适当格式的十进制数替换 {value:.2%}.由于我的模板可能包含大量 JavaScript 代码，我想避免使用 {{ 和 }} 转义大括号，因此使用 template.format(...) 直接不是一个选项.

I want to substitute {value:.2%} with some decimal number with the appropriate formatting. Since my template may contain a lot of JavaScript code, I want to avoid escaping the curly braces with {{ and }}, so using template.format(...) directly is not an option.

使用 Template(template).substitute(...) 似乎也不可能，因为我想要 value 的高级格式.

Using Template(template).substitute(...) also seems impossible because I want advanced formatting for value.

我可能可以用相应的 %(value)... 语法替换 {value:.2%}，然后使用 template % ....但我不喜欢这种语法，因为现实世界模板中的大多数变量不需要高级格式，所以我想保持占位符语法简单.

I could probably replace {value:.2%} with a corresponding %(value)... syntax and then use template % .... But I'm not a fan of this syntax because most of the variables in a real-world template won't need advanced formatting, so I want to keep the placeholder syntax simple.

所以我的问题是，是否可以在模板中使用自定义占位符，以便在必要时进行高级格式设置，即仅使用 {{value}} 或 [[value]] 还有 {{value:.2%}} 或 [[value:.2%]] ?

So my question is, is it possible to use custom placeholders in the template that would allow for advanced formatting when necessary, i.e. to have simply {{value}} or [[value]] but also {{value:.2%}} or [[value:.2%]] ?

最后，我想避免当模板包含占位符时 .format(...) 会产生的错误，例如 {{dont_want_this_located}}，传递的字典不包含值.也就是说，我只想替换某些占位符，而不是模板中出现的所有占位符.

Finally, I want to avoid errors that .format(...) would produce when the template contains placeholders, such as {{dont_want_this_substituted}}, for which the passed dictionary doesn't contain a value. That is, I want to only substitute only certain placeholders, not all that appear in the template.

为了实现我想要的，我可以先用正则表达式获取所有占位符，然后格式化它们的内容，最后在模板中进行替换.但我想知道是否存在更简单的解决方案.

Edit 2: To achieve what I want, I can grab all placeholders with a regular expression first, then format their contents and finally make the replacement in the template. But I wonder if an easier solution exists.

编辑 3: 有人建议我拆分模板以避免 format() 出现问题.然而，我想避免这种情况，因为模板实际上来自一个文件.

Edit 3: It was suggested that I split the template to avoid issues with format(). I would like to avoid this, however, because the template actually comes from a file.

推荐答案

只需预处理您的模板.例如，如果您希望 [[...]] 成为您的模板标记并保留单个 { 和 } 字符:

Simply preprocess your template. For example, if you want [[...]] to be your template markers and leave single { and } characters alone:

template = """
    <script>
        function work()
        {
            alert('bla');
        }
    </script>

    Success rate is [[value:.2%]] percent.
"""

result = template.replace("{", "{{").replace("}", "}}").replace("[[", "{").replace("]]", "}").format(value=0.8675309)

试图用不同数量的大括号来完成这一切是很棘手的，所以我肯定会使用其他一些字符.但是请注意，像 [[ 和 ]] 之类的东西可能会合理地出现在合法的 JavaScript 代码中.使用永远无法使用的东西可能会更好.

Trying to do it all with varying numbers of curly brackets is tricksy, so I would definitely use some other characters. Careful, though, things like [[ and ]] could reasonably occur in legitimate JavaScript code. Might be better to use something that never could.

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