passing optional arguments to a function in pandas

Question

this is my dataframe:

df = pd.DataFrame({'sym': ['msft', 'amd', 'bac', 'tsla'], 'close': [100, 30, 70, 80], 'sector': ['tech', 'tech', 'bank', 'auto'], 'watch_list': [1, 2, 2, 1]})

and this is the simpilified form of function that I want to use:

def add_volume(df):
  df['volume'] = [1000, 2000, 3000, 4000]
  return df

I want to pass two optional arguments(sector, watch_list) to my function that select the rows that I want for example if I call the function like this

add_volume (df, sector=['tech'], watch_list=[1])

It returns the first row.

And if I just call it like this

add_volume(df, watch_list = [1])

it returns the first and last row. I want both of the arguments to be optional.

def add_volume(df, sector=None, watch_list=None): Inside function check if arguments are not None and use them or not. — furas
– furas, Commented Jul 6, 2019 at 21:24

Anubhav Singh · Accepted Answer · 2019-07-06 21:53:22Z

You can use *args parameter. This allows you to add any number of parameters(optional parameters) after first parameter(in your case), which is compulsory.

Try this:

import pandas as pd
df = pd.DataFrame({'sym': ['msft', 'amd', 'bac', 'tsla'], 'close': [100, 30, 70, 80], 'sector': ['tech', 'tech', 'bank', 'auto'], 'watch_list': [1, 2, 2, 1]})

def add_volume(df, *args, **kwargs):
    sector = kwargs.get('sector', None)
    watch_list = kwargs.get('watch_list', None)

    df['volume'] = [1000, 2000, 3000, 4000]
    if sector and watch_list:
        return df[(df['sector']==sector) & (df['watch_list']==watch_list)]
    elif sector:
        return df[df['sector']==sector]
    elif watch_list:
        return df[df['watch_list']==watch_list]
    else:
        return df

print(add_volume(df, sector='tech', watch_list=1)) 
print(add_volume(df, watch_list=1)) 
print(add_volume(df, sector='tech'))
print(add_volume(df))

output:

   close sector   sym  watch_list  volume
0    100   tech  msft           1    1000

   close sector   sym  watch_list  volume
0    100   tech  msft           1    1000
3     80   auto  tsla           1    4000

   close sector   sym  watch_list  volume
0    100   tech  msft           1    1000
1     30   tech   amd           2    2000

   close sector   sym  watch_list  volume
0    100   tech  msft           1    1000
1     30   tech   amd           2    2000
2     70   bank   bac           2    3000
3     80   auto  tsla           1    4000

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