我如何将f字符串与变量一起使用，而不是与字符串文字一起使用? [英] How can i use f-string with a variable, not with a string literal?

问题描述

我想将f-string与我的字符串变量一起使用，而不要与由字符串文字"..."定义的字符串一起使用.

I want to use f-string with my string variable, not with string defined with a string literal, "...".

这是我的代码

name=["deep","mahesh","nirbhay"]
user_input = r"certi_{element}" # this string i ask from user  

for element in name:
    print(f"{user_input}")

此代码提供输出:

certi_{element}
certi_{element}
certi_{element}

但是我想要

certi_{deep}
certi_{mahesh}
certi_{nirbhay}

我该怎么做?

推荐答案

f"..."字符串非常有用，但是您没有文字，却有一个模板字符串放在单独的变量中.

f"..." strings are great when interpolating expression results into a literal, but you don't have a literal, you have a template string in a separate variable.

您可以使用 str.format() 将值应用于该模板:

You can use str.format() to apply values to that template:

name=["deep","mahesh","nirbhay"]
user_input = "certi_{element}" # this string i ask from user  

for value in name:
    print(user_input.format(element=value))

使用名称(例如{element})的字符串格式占位符不是变量.您可以在str.format()调用的关键字参数中为每个名称分配一个值.在上面的示例中，element=value传入value变量的值，以使用element填充占位符.

String formatting placeholders that use names (such as {element}) are not variables. You assign a value for each name in the keyword arguments of the str.format() call instead. In the above example, element=value passes in the value of the value variable to fill in the placeholder with the element.

与f-字符串不同，{...}占位符不是不是表达式，并且您不能在模板中使用任意Python表达式.这是一件好事，您不希望最终用户能够在您的程序中执行任意Python代码.有关详细信息，请参见 格式字符串语法文件 .

Unlike f-strings, the {...} placeholders are not expressions and you can't use arbitrary Python expressions in the template. This is a good thing, you wouldn't want end-users to be able to execute arbitrary Python code in your program. See the Format String Syntax documenation for details.

您可以输入任意数量的名称；字符串模板没有可以使用它们中的任何一个.如果将str.format()与**mapping调用约定结合使用，则可以使用任何词典作为值的来源:

You can pass in any number of names; the string template doesn't have to use any of them. If you combine str.format() with the **mapping call convention, you can use any dictionary as the source of values:

template_values = {
    'name': 'Ford Prefect',
    'number': 42,
    'company': 'Sirius Cybernetics Corporation',
    'element': 'Improbability Drive',
}

print(user_input.format(**template_values)

以上内容使用户可以随意使用模板中template_values中的任何名称.

The above would let a user use any of the names in template_values in their template, any number of times they like.

虽然您可以使用locals()和globals()来生成将变量名映射到值的字典，但我不建议您使用这种方法.使用上述专用的名称空间来限制可用的名称，并为最终用户记录这些名称.

While you can use locals() and globals() to produce dictionaries mapping variable names to values, I'd not recommend that approach. Use a dedicated namespace like the above to limit what names are available, and document those names for your end-users.

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