How to use Latex within an f-string expression in Matplotlib; no variables in equation

Question

I'm trying to make a title for a plot, but the title includes a variable, which I'm inserting using an f-string, but it also includes a Latex expression. I either get an error that f-string expressions do not take \ character, or else it's trying to read what's inside the equation as variables and complaining that it's not defined.

The code I'm trying looks something like this:

test = 'TEST'
plt.plot(1234,5678)
plt.title(f"This is a {test}: ${\sqrt{b/a}}$")
plt.show()

This code will give me the error: "f-string expression part cannot include a backslash", and when I try this (note the extra brackets):

test = 'TEST'
plt.plot(1234,5678)
plt.title(f"This is a {test}: ${{\sqrt{b/a}}}$")
plt.show()

I get this error: "name 'b' is not defined"

I want it to just show a square root of b/a, where b and a are just the letters, not variables, so that it looks something like the plot below:

but I can't seem to make it work with an f-string variable also in the title.

bgfvdu3w · Accepted Answer · 2022-06-28 20:02:47Z

3

It has to be done like this:

plt.title(f"This is a {test}: ${{\sqrt{{b/a}}}}$")

Since you need to use the { and } characters, they need to be doubled up so that they are interpreted as literal characters. This will prevent it from interpreting the contents between the brackets as a Python expression. Thus, it will no longer complain about the backslash or undefined variables.

Alternatively, it can be put in a separate string to avoid doubling up the brackets. This is more readable in my opinion.

tex = "${\sqrt{b/a}}$"
plt.title(f"This is a {test}: {tex}")

answered Jun 28, 2022 at 20:02

bgfvdu3w

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1 Comment

J. O'connor Over a year ago

That worked beautifully, thank you.

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