gistfile1.txt

Python 3.7.3 (default, Apr  3 2019, 05:39:12) 
Type 'copyright', 'credits' or 'license' for more information
IPython 7.5.0 -- An enhanced Interactive Python. Type '?' for help.

In [1]: dick = {'test1': {1,2,3,4,5,}, 'test2': {6,5,2,4,9,}, 'test3': {1, 4, 6, 9}}           

In [2]: set.intersection?                                                                      
Docstring:
Return the intersection of two sets as a new set.

(i.e. all elements that are in both sets.)
Type:      method_descriptor

In [3]: from functools import reduce                                                           

In [4]: reduce?                                                                                
Docstring:
reduce(function, sequence[, initial]) -> value

Apply a function of two arguments cumulatively to the items of a sequence,
from left to right, so as to reduce the sequence to a single value.
For example, reduce(lambda x, y: x+y, [1, 2, 3, 4, 5]) calculates
((((1+2)+3)+4)+5).  If initial is present, it is placed before the items
of the sequence in the calculation, and serves as a default when the
sequence is empty.
Type:      builtin_function_or_method

In [5]: reduce(set.intersection, dick.values())                                                
Out[5]: {4}