very simple calculator demo for a friend

original.py

note = '''Note: You can use 'plus','minus','times','divide' and
		'power' to calculate. Enter 'c' to clean and enter 'q'
		to quit.'''

#note_1="Note: You can use 'plus','minus','times','divide' and "
#note_2="'power' to calculate. Enter 'c' to clean and enter 'q' "
#note_3="to quit."
#note=note_1+note_2+note_3
note_4="Enter a algorithm(+ - * / ^):"
note_5='Enter a algorithm:'
note_6='Clean! Enter a number:'
note_7='Error! Enter number only:'
note_8='Enter next algorithm:'
note_9='Enter next number:'
print(note)

test_n=0

def calc(x,a,y):       
	if a == '+':
		u=x+y
	elif a == '-':
		u=x-y
	elif a == '*':
		u=x*y
	elif a == '/':
		u=x/y
	elif a == '^':
		u=x**y
	return u

def test_number(x):
	while x:
		if x == 'c':
			x=input(note_6)
			continue
		elif x == 'q':
			exit()
		try:
			x=int(x)+5
			x=x-5
			return x
			break
		except ValueError:
			x=input(note_7)
			
def test_algorithm(a,x):
	while a:
		if a == 'q':
			exit()
		elif a == 'c':
			x=input(note_6)
			test_number(x)
			a=input(note_5)
			continue
		elif a == '+':
			return a
			break
		elif a == '-':
			return a
			break
		elif a == '*':
			return a
			break
		elif a == '/':
			return a
			break
		elif a == '**':
			return a
			break
		else:
			a=input(note_5)
			continue

def test_next(y,a,x):
	while y:
		if y == 'q':
			exit()
		elif y == 'c':
			x=input(note_6)
			test_number(x)
			return x
			a=input(note_5)
			test_algorithm(a,x)
			return a
			y=input(note_9)
			continue
		try:
			y=int(y)+5
			y=y-5
			return y,a,x
			break
		except ValueError:
			y=input(note_7)

x=input('Enter a number:')
x=test_number(x)
a=input(note_4)
a=test_algorithm(a,x)
y=input(note_9)
y=test_next(y,a,x)
outcome=calc(x,a,y)
print("Outcome is "+str(outcome))
while True:
	x=outcome
	a=input(note_5)
	a=test_algorithm(a,x)
	y=input(note_9)
	y=test_next(y,a,x)
	outcome=calc(x,a,y)
	print('Outcome is '+str(outcome))

yet_another_one.py

# -*- coding: utf-8 -*-

import os, sys

formula = [None, None, None]
result = 0
operator = None

prompt = '''Note: You can use 'plus','minus','times','divide' and
'power' to calculate. Enter 'c' to clean and enter 'q'
to quit.'''

def will_clean(opt):
    if opt == 'c':
        print("Cleaned.")
        result = 0
        formula[0] = None
        return True
    

def will_quit(opt):
    if opt == 'q':
        print("Result:", result)
        os._exit(0)


def is_operator(opt):
    if opt not in ['+', '-', '*', '/']:
        return False

    return True


if __name__ == "__main__":
    print(prompt)
    
    while True:
        for o in formula:
            if o is not None:
                print(o) 

        x = input("Enter a number or operator(+ - * /): ")
        if will_clean(x):
            continue

        will_quit(x)

        if not x.isdigit() and not is_operator(x):
            print("Your input is invalid.")
            continue
        
        if formula[0] is None and not x.isdigit():
            print("You should input a digital first.")
            continue

        if formula[0] is None and x.isdigit():
            formula[0] = x # 为第一个算子赋值
            continue
        
        if formula[0].isdigit() and formula[1] is None:
            if is_operator(x):
                formula[1] = x # 为运算符赋值

            if x.isdigit():
                formula[0] = x # 更新第一个算子

            continue

        if formula[0].isdigit() and is_operator(formula[1]):
            if is_operator(x):
                formula[1] = x # 更新运算符
            
            if x.isdigit():
                formula[2] = x # 为第二个算子赋值

        if formula[0].isdigit() and is_operator(formula[1]) and formula[2].isdigit():
            if formula[1] == '+':
                result = int(formula[0]) + int(formula[2])
            if formula[1] == '-':
                result = int(formula[0]) - int(formula[2])
            if formula[1] == '*':
                result = int(formula[0]) * int(formula[2])
            if formula[1] == '/':
                result = int(formula[0]) / int(formula[2])

            print("%s %s %s = %s" % (formula[0], formula[1], formula[2], result))

            formula = [str(result), None, None] # 计算结果变为第一个算子，等待新的算式