Python | Find Symmetric Pairs in dictionary

Last Updated : 15 Oct, 2019

Sometimes, while working with Python dictionary, one can have a problem in which one desires to get key-value pairs that are symmetrical, i.e that has key-value pair of same value irrespective of the fact value is a key or value. Let’s discuss certain ways in which this task can be performed.

Method #1 : Using generator + loop

This task can be solved in brute force method using loops and generators by yielding at runtime the values of matching key-value pairs.

# Python3 code to demonstrate working of
# Find Symmetric Pairs in dictionary
# using generator + loop
  
# generator function to perform task
def find_sym_pairs(test_dict):
    for key in test_dict.keys():
        val = test_dict.get(key)
  
        if test_dict.get(val) == key:
            yield key, val
    return 
  
# Initializing dict
test_dict = {'a' : 1, 'b' : 2, 'c' : 3,  1 : 'a', 2 : 'b'}
  
# printing original dict 
print("The original dict is : " + str(test_dict))
  
# Find Symmetric Pairs in dictionary
# using generator + loop
res = []
for key, val in find_sym_pairs(test_dict):
    temp = (key, val)
    res.append(temp)
  
# printing result
print("The pairs of Symmetric values : " + str(res))

Output :

The original dict is : {'a': 1, 1: 'a', 'c': 3, 'b': 2, 2: 'b'}
The pairs of Symmetric values : [('a', 1), (1, 'a'), ('b', 2), (2, 'b')]

Method #2 : Using list comprehension

This task can also be performed as a one-liner using list comprehension as a shortened way of performing loop-based solution.

# Python3 code to demonstrate working of
# Find Symmetric Pairs in dictionary
# Using list comprehension
  
# Initializing dict
test_dict = {'a' : 1, 'b' : 2, 'c' : 3,  1 : 'a', 2 : 'b'}
  
# printing original dict 
print("The original dict is : " + str(test_dict))
  
# Find Symmetric Pairs in dictionary
# Using list comprehension
temp = [(key, value) for key, value in test_dict.items()]
res = [(x, y) for (x, y) in temp if (y, x) in temp]
  
# printing result
print("The pairs of Symmetric values : " + str(res))

Output :

The original dict is : {'a': 1, 1: 'a', 'c': 3, 'b': 2, 2: 'b'}
The pairs of Symmetric values : [('a', 1), (1, 'a'), ('b', 2), (2, 'b')]

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Python | Find Symmetric Pairs in dictionary