TypeError("'bool' object is not iterable",) when trying to return a Boolean

Question

I am having a strange problem. I have a method that returns a boolean. In turn I need the result of that function returned again since I cant directly call the method from the front-end. Here's my code:

# this uses bottle py framework and should return a value to the html front-end
@get('/create/additive/<name>')
def createAdditive(name):
    return pump.createAdditive(name)



 def createAdditive(self, name):
        additiveInsertQuery = """ INSERT INTO additives
                                  SET         name = '""" + name + """'"""
        try:
            self.cursor.execute(additiveInsertQuery)
            self.db.commit()
            return True
        except:
            self.db.rollback()
            return False

This throws an exception: TypeError("'bool' object is not iterable",)

I don't get this error at all since I am not attempting to "iterate" the bool value, only to return it.

If I return a string instead of boolean or int it works as expected. What could be an issue here?

Traceback:

Traceback (most recent call last):
  File "C:\Python33\lib\site-packages\bottle.py", line 821, in _cast
    out = iter(out)
TypeError: 'bool' object is not iterable

Solution

Look at the traceback:

Traceback (most recent call last):
  File "C:\Python33\lib\site-packages\bottle.py", line 821, in _cast
    out = iter(out)
TypeError: 'bool' object is not iterable

Your code isn't iterating the value, but the code receiving it is.

The solution is: return an iterable. I suggest that you either convert the bool to a string (str(False)) or enclose it in a tuple ((False,)).

Always read the traceback: it's correct, and it's helpful.

Comments

[zhangyangyu]

Post the whole traceback please.

[DominicM]

See edit for full traceback.

[DominicM]

String method worked but is very frustrating as I have to check for string not bool in front-end. Tulepe didn't work, is this correct syntax? [[[ return ((False,)) ]]] ? Also, is it common for frameworks with routing to require iterable data types? If it's just something bottle py does I would switch to web py...

[Marcin]

@DominicM No, you can't put a statement inside a list (or in fact, three lists). I think this is a common design. If you are trying to pass data to an XmlHTTPRequest, then I suggest you return AJAX (use the ajax module), and use an ajax parsing library on the client side.

[DominicM]

I guess I'm used to php being able to simply return then echo true/false. What do you mean by ajax parsing library? I am currently using javascript/jquery $.ajax call.

[Marcin]

@DominicM I mean a javascript library which will convert a string safely to the javascript objects it represents.

[DominicM]

It seems like overkill since it's just gonna be true/false or json data for other calls.

[Marcin]

@DominicM jquery.ajax will do it if you specify that you expect json. In any case, it's not overkill to avoid running arbitrary code. If you use eval, you're opening yourself up to XSS (and in general javascript injection attacks).

[DominicM]

Can name a specific library as an example?

[Marcin]

@DominicM I just told you: jquery.ajax has this functionality.

[DominicM]

You previous comment was misleading because I already said I was using jquery's $.ajax call...