expr2katex 0.1.0

Convert a Python expression string to a KaTeX string

expr2katex

Convert a Python expression string to a KaTeX string.

from expr2katex import expr2katex

katex, err = expr2katex("sin(a) + (c + 3) * b")
# katex → \sin\left(a\right)+\left(c+3\right)\times b
# err   → None

Features

• Zero dependencies — built on Python's standard ast module only
• Precedence-aware parenthesisation — reconstructs grouping from the AST structure, so (a + b) * c renders correctly without any string heuristics
• KaTeX-native functions — sin, cos, sqrt, log, etc. render with their native KaTeX commands (\sin, \sqrt{x}, …)
• Unknown functions fall back to \operatorname{foo} automatically
• Configurable division style — \frac{a}{b} or a \div b
• Symbol style overrides — control how variables and function names are rendered per symbol
• SyntaxError highlighting — invalid expressions return a KaTeX string with the offending token highlighted in red, designed for real-time UI previews

Installation

pip install expr2katex

Usage

Basic

from expr2katex import expr2katex

katex, err = expr2katex("sin(a) + b * c")
# \sin\left(a\right)+b\times c

Division style

expr2katex("a / b")                      # \frac{a}{b}  (default)
expr2katex("a / b", div_style="div")     # a \div b

Power and roots

expr2katex("a ** 2")          # a^{2}
expr2katex("sqrt(x)")         # \sqrt{x}
expr2katex("sqrt(x, 3)")      # \sqrt[3]{x}   (n-th root)

Symbol style overrides

from expr2katex import expr2katex, SymbolStyle

expr2katex("foo(x)", symbol_styles={
    "foo": SymbolStyle.TEXT,       # \text{foo}\left(x\right)
    "x":   SymbolStyle.BOLD,       # \boldsymbol{x}
})

SymbolStyle	Output	Default for
ITALIC	x	variables
OPERATORNAME	\operatorname{foo}	functions
TEXT	\text{foo}
BOLD	\boldsymbol{x}

SyntaxError highlighting

When the expression is invalid, expr2katex returns a KaTeX string with the offending token highlighted in red — useful for real-time formula editors.

katex, err = expr2katex("sin(a + (b * c")
# katex → \text{sin(a + }\textcolor{red}{\underbrace{\text{(}}}\text{b * c}
# err   → '(' was never closed

Choose between underbrace (default) and underline:

expr2katex("sin(a + (b * c", error_style="underline")

Raising on error

# SyntaxError is re-raised instead of being returned
expr2katex("sin(a + (b * c", raise_on_error=True)
# SyntaxError: '(' was never closed

# All non-SyntaxError exceptions are always raised regardless of raise_on_error.

API reference

def expr2katex(
    expr: str,
    raise_on_error: bool = False,
    div_style: Literal["frac", "div"] = "frac",
    symbol_styles: dict[str, SymbolStyle] | None = None,
    error_style: Literal["underbrace", "underline"] = "underbrace",
) -> tuple[str, str | None]: ...

Parameter	Type	Default	Description
expr	str	—	Python expression string to convert
raise_on_error	bool	False	Re-raise SyntaxError instead of returning highlighted KaTeX
div_style	"frac" | "div"	"frac"	Division rendering style
symbol_styles	dict[str, SymbolStyle] | None	None	Per-symbol style overrides
error_style	"underbrace" | "underline"	"underbrace"	Error highlight decoration

Returns (katex: str, err: str | None) — err is None on success, or SyntaxError.msg on failure.

Supported operators

Python	KaTeX output
+	a+b
-	a-b
*	a\times b
/	\frac{a}{b}
//	\lfloor\frac{a}{b}\rfloor
%	a\bmod b
**	a^{b}
-x	-x
+x	x (omitted)

KaTeX-native functions

The following function names are rendered with their native KaTeX command (\sin, \cos, …). All other names fall back to \operatorname{name}.

sin cos tan arcsin arccos arctan sinh cosh tanh log ln exp min max gcd lcm det dim sqrt

sqrt uses the dedicated \sqrt{x} template. Pass a second argument for n-th roots: sqrt(x, n) → \sqrt[n]{x}.

License

MIT