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, p2
f2(**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):
- The function can have parameters that are not included in the dictionary
- You can not override a parameter that is already in the dictionary
- 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 inspect
In[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.