Add MathREPL, a math expression evaluator using eval()

Author: lpozo

python-eval-mathrepl/mathrepl.py

@@ -0,0 +1,80 @@
+#!/usr/bin/env python3
+
+# File: mathrepl.py
+
+"""MathREPL, a math expression evaluator using Python's eval() and math."""
+
+import math
+
+__version__ = "1.0"
+__author__ = "Leodanis Pozo Ramos"
+
+ALLOWED_NAMES = {
+    name: obj
+    for name, obj in math.__dict__.items()
+    if "__" not in name
+}
+
+PS1 = "mr>>"
+
+WELCOME = f"""
+MathREPL {__version__}, your Python math expressions evaluator!
+Enter a valid math expression after the prompt "{PS1}".
+Type "help" for more information.
+Type "quit" or "exit" to exit.
+"""
+
+USAGE = f"""
+Usage:
+Build math expressions using numeric values and operators.
+Use any of the following functions and constants:
+
+{', '.join(ALLOWED_NAMES)}
+"""
+
+
+def evaluate(expression: str) -> float:
+    """Evaluate a math expression."""
+    # Compile and validate syntax
+    try:
+        code = compile(expression, "<string>", "eval")
+    except SyntaxError:
+        raise SyntaxError("Invalid input expression")
+
+    # Validate allowed names
+    for name in code.co_names:
+        if name not in ALLOWED_NAMES:
+            raise NameError(f'The use of "{name}" is not allowed')
+
+    return eval(code, {"__builtins__": {}}, ALLOWED_NAMES)
+
+
+def main() -> None:
+    """Main loop: Read and evaluate user input."""
+    print(WELCOME)
+    while True:
+        # Read user's input
+        try:
+            expression = input(f"{PS1} ")
+        except (KeyboardInterrupt, EOFError):
+            raise SystemExit()
+
+        # Handle special commands
+        if expression.lower() == "help":
+            print(USAGE)
+            continue
+        if expression.lower() in {"quit", "exit"}:
+            raise SystemExit()
+
+        # Evaluate the expression
+        try:
+            result = evaluate(expression)
+        except Exception as err:
+            print(err)
+
+        # Print the result
+        print(f"The result is: {result}")
+
+
+if __name__ == "__main__":
+    main()