Passing a dictionary to a function as keyword parameters Passing a dictionary to a function as keyword parameters python python

Passing a dictionary to a function as keyword parameters


Figured it out for myself in the end. It is simple, I was just missing the ** operator to unpack the dictionary

So my example becomes:

d = dict(p1=1, p2=2)def f2(p1,p2):    print p1, p2f2(**d)


In[1]: def myfunc(a=1, b=2):In[2]:    print(a, b)In[3]: mydict = {'a': 100, 'b': 200}In[4]: myfunc(**mydict)100 200

A few extra details that might be helpful to know (questions I had after reading this and went and tested):

  1. The function can have parameters that are not included in the dictionary
  2. You can not override a parameter that is already in the dictionary
  3. The dictionary can not have parameters that aren't in the function.

Examples:

Number 1: The function can have parameters that are not included in the dictionary

In[5]: mydict = {'a': 100}In[6]: myfunc(**mydict)100 2

Number 2: You can not override a parameter that is already in the dictionary

In[7]: mydict = {'a': 100, 'b': 200}In[8]: myfunc(a=3, **mydict)TypeError: myfunc() got multiple values for keyword argument 'a'

Number 3: The dictionary can not have parameters that aren't in the function.

In[9]:  mydict = {'a': 100, 'b': 200, 'c': 300}In[10]: myfunc(**mydict)TypeError: myfunc() got an unexpected keyword argument 'c'

As requested in comments, a solution to Number 3 is to filter the dictionary based on the keyword arguments available in the function:

In[11]: import inspectIn[12]: mydict = {'a': 100, 'b': 200, 'c': 300}In[13]: filtered_mydict = {k: v for k, v in mydict.items() if k in [p.name for p in inspect.signature(myfunc).parameters.values()]}In[14]: myfunc(**filtered_mydict)100 200

Another option is to accept (and ignore) additional kwargs in your function:

In[15]: def myfunc2(a=None, **kwargs):In[16]:    print(a)In[17]: mydict = {'a': 100, 'b': 200, 'c': 300}In[18]: myfunc2(**mydict)100

Notice further than you can use positional arguments and lists or tuples in effectively the same way as kwargs, here's a more advanced example incorporating both positional and keyword args:

In[19]: def myfunc3(a, *posargs, b=2, **kwargs):In[20]:    print(a, b)In[21]:    print(posargs)In[22]:    print(kwargs)In[23]: mylist = [10, 20, 30]In[24]: mydict = {'b': 200, 'c': 300}In[25]: myfunc3(*mylist, **mydict)10 200(20, 30){'c': 300}


In python, this is called "unpacking", and you can find a bit about it in the tutorial. The documentation of it sucks, I agree, especially because of how fantasically useful it is.


matomo