Append string variable to LaTeX based raw string

Trying to append an integer as per this post and this post.

Requirement:

from IPython.display import display, Markdown
N = 128
text = r'$QFT=\frac{1}{\sqrt{'+str(N)+'}} \begin{bmatrix}'

text = text + r'1 & 2 \\ 3 & 4 \\'
text = text + r' \end{bmatrix}$'
display(Markdown(text))

Tried: IndexError: Replacement index 1 out of range for positional args tuple

N = str(128)
text = r'$QFT=\frac{1}{\sqrt{N}} \begin{bmatrix}'.format(N)

But either of these don’t work. Note, here text is LaTeX based string.

>Solution :

Double each curly bracket if it’s a part of the string:

> N = 128
> text = r"$QFT = \frac{{1}}{{\sqrt{{{0}}}}} \begin{{bmatrix}}".format(N)
> print(text)
$SQFT = \frac{1}{\sqrt{128} \begin{bmatrix}

In case you want to use a parameter N in the string, then use the explicit parameter format(N=N) to get the same effect:

> text = r"$QFT = \frac{{1}}{{\sqrt{{{N}}}}} \begin{{bmatrix}}".format(N=N)
> print(text)
$SQFT = \frac{1}{\sqrt{128} \begin{bmatrix}