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I'm using python to generate LaTeX code (long story - I need to produce 120-odd unique exams).

This means that I have lots of strings that have \ or { or } etc. So I'm making them literals. However, I also want to have Python calculate numbers and put them in. So I might have a string like: r"What is the domain of the function $\exp{-1/(VARIABLE - x^2+y^2)}$?" which I want to write to a file. But I want VARIABLE to be a random numerical value. The question isn't how to calculate VARIABLE, but rather is there a clean way to put VARIABLE into the string, without something like: r"What is the domain of the function $\exp{-1/(" + str(VARIABLE) + r"- x^2+y^2)}$?"

I'm going to be doing this a lot, so if it's doable, that would be great. I've got Python 3.5.2.

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    "So I'm making them literals" sounds kind of like you might have the wrong idea of what "string literal" means. It sounds like you might have gotten "raw string literal" and "string literal" mixed up. Commented Jun 4, 2020 at 6:18
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    r'whatever' is a raw string literal, but 'whatever' is still a string literal. Commented Jun 4, 2020 at 6:18
  • yes, I realize that they are the same thing (as in I know python does not distinguish), but I think (assumed?) everyone knew what I meant in terms of how I'm entering them. Commented Jun 4, 2020 at 6:43

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Python still supports the string substitution operator %: 

r"What is ... $\exp{-1/(%s - x^2+y^2)}$?" % str(VARIABLE)

You can be more specific if you know the type of the variable, e.g.:

r"What is ... $\exp{-1/(%f - x^2+y^2)}$?" % VARIABLE

More than one variable can be substituted at once:

r"$\mathrm{x}^{%i}_{%i}$" % (VAR1, VAR2)

This will work as long as your strings do not have LaTeX comments that, incidentally, also begin with a %. If that's the case, replace % with %%.

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I'm very partial to f-strings, since the variable names appear where the values eventually will.

You can have raw f-strings, but you'll need to escape curly braces by doubling them ({{), which could get confusing if you're writing out complex LaTex.

To get the string What is ... $\exp{-1/(10 - x^2+y^2)}$?:

VARIABLE = 10 rf"What is ... $\exp{{-1/({VARIABLE} - x^2+y^2)}}$?"
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FYI: f-strings appeared in 3.6. The OP uses 3.5.2.
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You may be able to use the % formatting 

variable = 10 "What is the domain of the function $exp{-1/x + %d}." % (variable)
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If your goal is to not break up the string you could do this to replace the variable with your variable value and also be able to use %s in your string:

r"What is the domain of the function $\exp{-1/(VARIABLE - x^2+y^2)}$?".replace("VARIABLE", str(VARIABLE))

If you need multiple values you can use this:

variable_list = [2, 3] ''.join([e+str(variable_list[c]) if c<len(variable_list) else str(e) for c,e in enumerate(r"What is the domain of the function $\exp{-1/(VARIABLE - x^2+y^2)}$?".split("VARIABLE"))])
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.replace("VARIABLE", str(VARIABLE)) is a more natural solution.

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