---input---
f"a={d['a']}"

---tokens---
'f'           Literal.String.Affix
'"'           Literal.String.Double
'a='          Literal.String.Double
'{'           Literal.String.Interpol
'd'           Name
'['           Punctuation
"'"           Literal.String.Single
'a'           Literal.String.Single
"'"           Literal.String.Single
']'           Punctuation
'}'           Literal.String.Interpol
'"'           Literal.String.Double
'\n'          Text.Whitespace