how to pass named parameters to function in python

Question

I have a function A with two named parameters and a function B that will optimize the result of A, changing its arguments. The algorithm is the same regardless I optimize the first or the second parameter. Can I pass to B the name and the value of needed parameter? The question raised while looking at scikit-learn functions of machine learning.

I want something like this:

def A(p1 = 0, p2 = 0):
   print(p1 + p2)
def B(par_name, par_val):
    ...

B will call A with given parameter.

B("p1", 1) => A(p1 = 1, p2 = 0)
B("p2", 1) => A(p1 = 0, p2 = 1)

Joe Platano · Accepted Answer · 2017-10-10 05:51:48Z

2

You can call A with the keyword argument that you need. In a similar case i put the arguments from the calling function in a dict and pass his to the called function

def A(p1 = 0, p2 = 0):
  print(str(p1) + str(p2))
def B(par_name, par_val):
   para_dict = dict()
   para_dict[para_name] = para_val
   A(**para_dict)

Please see Key Word Arguments in the python docs for more details.

another way is, that your dict already has all keys p1, p2 with its default values and you are just update the key you want and pass it to A

para_dict = {"p1":0,"p2":0}

and it might be better to loop through the arguments in A

edited Oct 10, 2017 at 5:51

answered Oct 10, 2017 at 5:44

Joe Platano

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Comments

ruX · Accepted Answer · 2017-10-23 22:42:59Z

0

Yes, it is possible to use named arguments when calling another functions:

 def A(p1, p2):
   print("p1=%s, p2=%s" % (p1, p2))

 def B():
   A(p2="two", p1="one")

 >>> B()
 p1=one, p2=two

edited Oct 23, 2017 at 22:42

answered Sep 22, 2017 at 10:33

ruX

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2 Comments

NastyaNirvana Over a year ago

Thanks, but I want a bit another effect, see edited question.

ruX Over a year ago

IFrom you example it's not clear how does p1 become 1 and 1(2nd arg) become 0

Bab_iam · Accepted Answer · 2017-10-25 12:19:21Z

0

The number and names of the parameters are fixed? If so, the best way is passing a dict as Joe Platano has mentioned. Otherwise you can also do

>>> def A(p={}):
       # to print?
...    print(p.get('p1',0),' + ',p.get('p2',0))
       # or to compute?
...    print(p.get('p1',0) + p.get('p2',0))
...
>>> def B(key, value):
...     A(p={key:value})
...
>>> B('p1',1)
1  +  0
1
>>> B('p2',1)
0  +  1
1

answered Oct 25, 2017 at 12:19

Bab_iam

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