如何将字符串转换为f字符串? [英] How do I convert a string into an f-string?

问题描述

我正在阅读有关Python的新内容的 博客 f弦，它们看起来真的很整齐.但是，我希望能够从字符串或文件中加载f字符串.

I was reading this blog on python's new f-strings and they seem really neat. However, I want to be able to load an f-string from a string or file.

我似乎找不到任何执行此操作的字符串方法或其他函数.

I can't seem to find any string method or other function that does this.

来自上面链接中的示例:

From the example in my link above:

name = 'Fred'
age = 42
f"My name is {name} and I am {age} years old"

'My name is Fred and I am 42 years old'

但是如果我有一个字符串s怎么办?我希望能够修饰s，如下所示:

But what if I had a string s? I want to be able to eff-ify s, something like this:

name = 'Fred'
age = 42
s = "My name is {name} and I am {age} years old"
effify(s)

---

结果证明，我已经可以执行与str.format类似的操作，并获得更高的性能.即:

---

Turns out I can already perform something similar to str.format and garner the performance pick up. Namely:

format = lambda name, age: f"My name is {name} and I am {age} years old"
format('Ted', 12)

'My name is Ted and I am 12 years old'

推荐答案

f字符串是代码.不仅以安全的方式(当然，字符串文字就是代码)，而且以危险的任意代码执行方式.这是有效的f字符串:

f-strings are code. Not just in the safe, "of course a string literal is code" way, but in the dangerous, arbitrary-code-execution way. This is a valid f-string:

f"{__import__('os').system('install ransomware or something')}"

，它将在评估后执行任意的shell命令.

and it will execute arbitrary shell commands when evaluated.

您在问如何获取从文本文件加载的字符串并将其作为代码进行评估，答案归结为eval.当然，这是安全风险，并且可能是个坏主意，因此，我建议不要尝试从文件中加载f字符串.

You're asking how to take a string loaded from a text file and evaluate it as code, and the answer boils down to eval. This is of course a security risk and probably a bad idea, so I recommend not trying to load f-strings from files.

如果要从文件加载f字符串f"My name is {name} and I am {age} years old"，请实际放置

If you want to load the f-string f"My name is {name} and I am {age} years old" from a file, then actually put

f"My name is {name} and I am {age} years old"

文件中的

，f和引号以及所有内容.

in the file, f and quotation marks and all.

从文件中读取，编译并保存(因此eval不必每次都重新编译):

Read it from the file, compile it and save it (so eval doesn't have to recompile it every time):

compiled_fstring = compile(fstring_from_file, '<fstring_from_file>', 'eval')

并使用eval进行评估:

formatted_output = eval(compiled_fstring)

如果这样做，请非常注意从中加载f字符串的来源.

If you do this, be very careful about the sources you load your f-strings from.

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