Question

I’m working on developing a mini-language in Python (not really, just a few commands for a personal project).

Here’s the code:

class FlashCard:
    def __init__(self):
        self.commands = {'addQuestion':self.addQuestion}
        self.stack = []
        self.questions = {}


    def addQuestion(self):
        question = self.stack.pop()
        answer = input(question)


    def interpret(self,expression):
        for token in expression.split():
            if token in self.commands:
                operator = self.commands[token]
                operator()
            else:
                self.stack.append(token)

i = FlashCard()
i.interpret('testing this addQuestion')

The interpret function will only pull the last word (this) from the string. Is there a way to make it pull the entire line?

Thank you!

Answer 1

Since stack is a list, and you are calling the pop method without arguments, what you will get is the last elements in the list. You probably want to transform the list in a space-separated string, instead:

def addQuestion(self):
    question = ' '.join(self.stack)
    answer = input(question)

Observe that the side effect of pop and join are different. pop will modify the original list:

>>> stack = ['testing', 'this']
>>> stack.pop()
'this'
>>> stack
['testing']

while join won’t:

>>> stack = ['testing', 'this']
>>> ' '.join(stack)
'testing this'
>>> stack
['testing', 'this']

---

Edit (see comments of OP below): To parse multiple lines / commands in the same input, you could do different things. The easiest that comes to my mind: flush the stack after the call to operator():

if token in self.commands:
    operator = self.commands[token]
    operator()
    self.stack = []

---

Edit 2 (see my own comment below): Here’s the complete example using a list of strings:

class FlashCard:
    def __init__(self):
        self.commands = {'addQuestion':self.addQuestion}

    def addQuestion(self, phrase):
        answer = raw_input(phrase)

    def interpret(self, expressions):
        for expression in expressions.split('\n'):
            phrase, command = expression.rsplit(' ', 1)
            if command in self.commands:
                operator = self.commands[command]
                operator(phrase)
            else:
                raise RuntimeError('Invalid command')

expressions = '''testing this addQuestion
testing that addQuestion
testing error removeQuestion'''
i = FlashCard()
i.interpret(expressions)

HTH!