Passing variable arguments : python

Question

I want to write a code that takes file and class names, and operates over it. An example will explain it much more clearly than I possibly can:

I have a file test.py that goes as:

import pandas as pd
from preProcess import preProcess
from visualise import visualise

df=pd.read_csv('input.csv')

li1=["preProcess","visualise"]
li2=["minMax","pca"]

for i in range(len(li1)):
    x = getattr(getattr(__import__(li1[i]),li1[i]), li2[i])
    a=x(df)
    # does some more stuff...

li1 contains name of the modules and li2 contains the name of the classes in the corresponding modules.

To make it a bit clearer, preProcess.py goes as:

class minMax():
    def __init__(df):
    # does something

and visualise.py goes as:

class pca():
    def __init__(df):
    # does something

The line x = getattr(getattr(__import__(li1[i]),li1[i]), li2[i]) gives me the classes minMax and pca.

Now the thing is that this code works perfectly fine if __init__ takes only one argument. But, what if it requires more than 1 arguments? For eg., pca could have been:

class pca():
    def __init__(df,metaData):
    # does something

What should I do in such a case? Any help would be appreciated.

If the question is not clear, please drop a comment. I would provide a more detailed explanation then. Thanks...

Eugene Ghanizadeh Khoub · Accepted Answer · 2019-06-06 12:43:50Z

1

perhaps you should utilize the spread operator. maybe this snippet helps:

class X:
  def __init__(self, a, b):
    self.a = a
    self.b = b

args = [2, 'hellow']
x = X(*args)

EDIT: this is just an outline of the general approach. for a more comprehensive overview of how this approach is applicable to this specific problem, please check the discussion on this answer.

edited Jun 6, 2019 at 12:43

answered Jun 6, 2019 at 10:12

Eugene Ghanizadeh Khoub

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7 Comments

MEdwin Over a year ago

i wonder who is marking down without commenting. It really doesnt help anyone.

Ankit Kumar Over a year ago

I appreciate the answer, but there will be a problem with args in my implementation. There can be about 100 such function, that too overloaded. It won't be feasible for me... (PS: I didn't downvote)

Eugene Ghanizadeh Khoub Over a year ago

@MEdwin yeah its seems weird, but anyways internet is going to internet.

Ankit Kumar Over a year ago

@EugeneGhanizadehKhoub I want the code to be scalable. I have certain classes with that have overloaded methods, i.e, f(a,b=None). To make a list for args, I'll need to check if the user passes b or not. What you are saying is 100% correct, but I cannot use if-else statements in my code due to scalability issue.

Ankit Kumar Over a year ago

@EugeneGhanizadehKhoub I modified my code to take a dataframe and a dictionary as input (for all the functions). In that dictionary, I can beforehand add all of the variables, and use them in a function, if needed. Accepting your answer because it was really helpful to come up with this idea. But please edit your answer to include this idea. To clarify, I changed test.py to have the line a=x(df,dict) and all functions f to f(df,*args). Then, I'm using args in the functions I need (and it works as I want it to). Thanks...

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