Project 3 · Practice Projects
Build a command-line calculator that parses infix expressions (+, -, *, /, **, %) and handles division-by-zero and invalid input gracefully.
Difficulty: Lv ★ | Prerequisites: Basics Week 4 + Week 9
Menu-based arithmetic operations + cumulative results
**, %eval prohibited)Try the assignment yourself first — comparing your attempt with a working solution is where most of the learning happens.
"""CLI Calculator — Menu Type + Cumulative Results"""
OPS = {
"1": ("+", lambda a, b: a + b),
"2": ("-", lambda a, b: a - b),
"3": ("*", lambda a, b: a * b),
"4": ("/", lambda a, b: a / b if b != 0 else None),
}
def main():
history = []
last = None
while True:
print("[Menu] 1.+ 2.- 3.* 4./ 5.Use previous result 6.Exit")
choice = input("Select:").strip()
if choice == "6":
break
if choice not in OPS:
print("Invalid selection"); continue
try:
if last is not None and input(f"First number (previous result {last}):").strip() == "":
a = last
else:
a = float(input("First number:"))
b = float(input("Second number:"))
except ValueError:
print("Numbers only"); continue
symbol, fn = OPS[choice]
result = fn(a, b)
if result is None:
print("Cannot divide by 0")
continue
print(f"Result: {a} {symbol} {b} = {result}")
history.append(f"{a} {symbol} {b} = {result}")
last = result
print("[Operation History]")
for h in history:
print(f" {h}")
if __name__ == "__main__":
main()Work through the Python Series track on your own, or join a guided cohort at our Pitampura campus and online.