Python Defining parameters for nested function on outer function call

Question

I have the following function:

def splot (self,what):
    df = pd.DataFrame((self.spec[what]).compute()).plot()
    plt.show()
    return df

I want to be able to pass parameters to the .plot() method when I call the splot function, like below:

def splot (self,what,arg=None):
    df = pd.DataFrame((self.spec[what]).compute()).plot(arg)
    plt.show()
    return df

So when I call splot, I give it two arguments: 'what' (a string), and the arguments I want the plot command to take.

However, this doesn't work: if I pass the argument as a string, I get a KeyError, and if not, it throws a variable error. I have a feeling that *args should be involved somewhere, but not sure how to use it in this instance.

Have you called method like this Obj.splot (what, arg="x") ? — Muthuraj S
– Muthuraj S, Commented Aug 13, 2018 at 11:26

Laurent H. · Accepted Answer · 2018-08-13 12:29:43Z

1

Indeed, as you are guessing, you have to use the unpacking operator *. Here is an example of code close to yours in order to explain:

class myClass:

    def myPlot(self, x=None, y=None):
        print("myPlot:", x)
        print("myPlot:", y)

    def myFunc(self, what, *args, **kwargs):
        print(what)         # 'toto'
        print(args)         # tuple with unnamed (positional) parameters
        print(kwargs)       # dictionary with named (keyword) parameters
        self.myPlot(*args, **kwargs)   # use of * to unpack tuple and ** to unpack dictionary


myObject = myClass()
myObject.myFunc("toto", 4, 12)         # with positional arguments only
myObject.myFunc("toto", x = 4, y = 12) # with keyword arguments only
myObject.myFunc("toto", 4, y = 12)     # with both

So you should write your code like this:

def splot (self, what, *args, **kwargs):
    df = pd.DataFrame((self.spec[what]).compute()).plot(*args, **kwargs)
    plt.show()
    return df

edited Aug 13, 2018 at 12:29

answered Aug 13, 2018 at 11:27

Laurent H.

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4 Comments

nothingtoseehere Over a year ago

So that only brings along strings. What I'm trying to do is use the parameters of the pd.DataFrame.plot command. Is that just use **kwargs instead, or is it more complex?

Laurent H. Over a year ago

@nothingtoseehere OK my first solution worked only with unnamed positional arguments. I have updated my post to work with named arguments either.

nothingtoseehere Over a year ago

Yep, that works fine. Needs both *args and **kwargs for **kwargs to work for some reason, but it works.

Laurent H. Over a year ago

Cool. if you use only keywords arguments, you don't need *args. Please consider accepting this answer (by clicking on Accept) if it answers your request.

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