Python | Substring Key match in dictionary

Sometimes, while working with dictionaries, we might have a use case in which we are not known the exact keys we require but just a specific part of keys that we require to fetch. This kind of problem can arise in many applications. Let’s discuss certain ways in which this problem can be solved. 

Method #1 : Using items() + list comprehension The combination of above method can be used to perform this particular task in which we just access the key value pairs using the items function and list comprehension helps in the iteration and access logic. 

Python3

# Python3 code to demonstrate working of
# Substring Key match in dictionary
# Using items() + list comprehension

# initializing dictionary
test_dict = {'All': 1, 'have': 2, 'good': 3, 'food': 4}

# initializing search key string
search_key = 'ood'

# printing original dictionary
print("The original dictionary is : " + str(test_dict))

# Using items() + list comprehension
# Substring Key match in dictionary
res = [val for key, val in test_dict.items() if search_key in key]

# printing result
print("Values for substring keys : " + str(res))

Output : 

The original dictionary is : {'All': 1, 'food': 4, 'have': 2, 'good': 3}
Values for substring keys : [4, 3]

Method #2 : Using dict() + filter() + lambda

The combination of above functions can be used to perform this particular task. In this, the dict and filter function is used to convert the result to dictionary and query for the substring in list respectively. The lambda performs the task of accessing all key-value pairs. 

Python3

# Python3 code to demonstrate working of
# Substring Key match in dictionary
# Using dict() + filter() + lambda

# initializing dictionary
test_dict = {'All': 1, 'have': 2, 'good': 3, 'food': 4}

# initializing search key string
search_key = 'ood'

# printing original dictionary
print("The original dictionary is : " + str(test_dict))

# Using dict() + filter() + lambda
# Substring Key match in dictionary
res = dict(filter(lambda item: search_key in item[0], test_dict.items()))

# printing result
print("Key-Value pair for substring keys : " + str(res))

Output : 

The original dictionary is : {'have': 2, 'good': 3, 'food': 4, 'All': 1}
Key-Value pair for substring keys : {'good': 3, 'food': 4}

Method #3: Using keys() and find() methods

Python3

# Python3 code to demonstrate working of
# Substring Key match in dictionary

# initializing dictionary
test_dict = {'All': 1, 'have': 2, 'good': 3, 'food': 4}

# initializing search key string
search_key = 'ood'

# printing original dictionary
print("The original dictionary is : " + str(test_dict))
res = []
for i in test_dict.keys():
    if(i.find(search_key) != -1):
        res.append(test_dict[i])

# printing result
print("Values for substring keys : " + str(res))

Output

The original dictionary is : {'All': 1, 'have': 2, 'good': 3, 'food': 4}
Values for substring keys : [3, 4]

Method #4: Using re.search()
This method uses the re.search() function from the re module to check if the search key is a substring of any of the keys in the dictionary. If it is, the corresponding value is added to a list.

Python3

# Python3 code to demonstrate working of
# Substring Key match in dictionary
# Using re.search()

import re

# initializing dictionary
test_dict = {'All': 1, 'have': 2, 'good': 3, 'food': 4}

# initializing search key string
search_key = 'ood'

# printing original dictionary
print("The original dictionary is : " + str(test_dict))

# Using re.search()
# Substring Key match in dictionary
res = [val for key, val in test_dict.items() if re.search(search_key, key)]

# printing result
print("Values for substring keys : " + str(res))
#This code is contributed by Edula Vinay Kumar Reddy

Output

The original dictionary is : {'All': 1, 'have': 2, 'good': 3, 'food': 4}
Values for substring keys : [3, 4]

Method #4 has a time complexity of O(n) and  Auxiliary space of O(n) where n is the number of items in the dictionary