Hum-cal.py

def convert_to_words(input_message):
    # Vocabulary
    words = {
        '0': 'zero',
        '1': 'one',
        '2': 'two',
        '3': 'three',
        '4': 'four',
        '5': 'five',
        '6': 'six',
        '7': 'seven',
        '8': 'eight',
        '9': 'nine',
        '10': 'ten',
        '11': 'eleven',
        '12': 'twelve',
        '13': 'thirteen',
        '=': 'equals',
        '-': 'minus',
        '+': 'plus',
        '*': 'times',
        '/': 'divided by',
        '.': 'point',
        ',': 'comma',
        ' ': ' '
    }

    # Check if the input message is valid
    if type(input_message) == str:
        print(input_message)
        digits = input_message.split()
        print(digits)
        for element in digits:
            if len(element) <= 1:
                input_message = input_message.replace(element, words[element])
            elif len(element) == 2:
                print (element, words[element])
                # input_message = input_message.replace(element, words[element])
        return input_message
    else:
        return 'invalid input'


print(convert_to_words(1))
print(convert_to_words('3 + 7 = 10'))
print(convert_to_words('5 * 7 = 35'))