How to allow custom Class parameter to be tab-completed in ipython?

Question

for example, if I have the following classes

class Part(object):
    def __init__(self,part_number,description,rev=None,color=None):
        self.dims = {}
        self.dim_id = 0
        self.rev = rev
        if type(color) is tuple:
            self.color=(color[0]/255.,color[1]/255.,color[2]/255.)
        else:
            self.color = color

     def add_dimension(self,description,value,tol,tol_type = 'sym',dwg_sheet = None, dwg_zone = None,quality = 3):
        self.dims[description] = Dimension(description=description,part=self,value=value,tol=tol,tol_type=tol_type,quality=quality,dwg_sheet=None,dwg_zone=None)


    def __getattr__(self, description):
        return self.dims[description]

class Dimension(object):
    def __init__(self,part,value,tol,tol_type = 'sym', dwg_sheet = None, dwg_zone = None, quality = 3, description = None):
        self.value = value
        self.part=part
        self.tol = tol
        self.tol_type = tol_type
        self.description = description
        self.quality = quality
        self.sigma = self.tol/float(quality)


    def __str__(self):
    return self.description

Then I run the following code:

a = Part('pn','this is a part')
a.add_dimension('this_is_a_dimension',1.00,0.05)
print a.this_is_a_dimension

It returns:

this_is_a_dimension

the problem is that when I try to do tab completion after typing "a.", I get only the following options

a.add_dimension
a.color
a.dim_id
a.dims
a.rev

I would like to be able to tab-complete to see my new parameter. It would be similar to how column names in Pandas Dataframes work.

Any thoughts?

Answer 1

You can. You must implement a __dir__() method for your class, as discussed here.

This is an example of it working:

class bar(object):
    def __init__(self,):
        self.a = 4
        self._morelements=['b']
    def __dir__(self):
        return sorted(set(dir(type(self)) + list(self.__dict__) + self._morelements))

foo=bar()

Now if you write foo. and press TAB in Ipython you will have as available members both a and b, although b does not exist.

The code for __dir__() and a discussion of the limitations of this approach is here. In your case, you want to add description to the list self._morelements inside the function add_dimension().

EDIT: And of course you also need to initialize self._morelements=[] in the __init__(), and add the __dir__() function of the example above to your class Part

Answer 2

Python is interpreted. So, it only knows about code it has already interpreter. An example of this is: if you try to run the code you posted, you will get an error at the line:

self.dims[description] = Dimension(description=description,part=self,value=value,tol=tol,tol_type=tol_type,quality=quality,dwg_sheet=None,dwg_zone=None)

the error: global name 'Dimension' is not defined. That's because you define the class Dimension after. At the time the interpreter reach that line, the class Dimension does not exists.

this_is_a_dimension attribute of a only exists at run time and after the line:

a.add_dimension('this_is_a_dimension',1.00,0.05)

For accomplish what you want, you'll need some IDE that interprets the python code at edit time.