Python – Unpacking Values in Strings

Given a dictionary, unpack its values into a string.

Input : test_str = “First value is {} Second is {}”, test_dict = {3 : “Gfg”, 9 : “Best”} 
Output : First value is Gfg Second is Best 
Explanation : After substitution, we get Gfg and Best as values. 

Input : test_str = “First value is {} Second is {}”, test_dict = {3 : “G”, 9 : “f”} 
Output : First value is G Second is f. 
Explanation : After substitution, we get G and f as values.

Method 1: Using format() +  * operator + values()

The combination of above functions can be used to solve this problem. In this, we use format to map required value with braces in string. The * operator is used to unpack and assign. The values are extracted using values().

Python3

# Python3 code to demonstrate working of
# Unpacking Integer Keys in Strings
# Using format() + * operator + values()

# initializing string
test_str = "First value is {} Second is {} Third {}"

# printing original string
print("The original string is : " + str(test_str))

# initializing dictionary
test_dict = {3 : "Gfg", 4 : "is", 9 : "Best"}

# using format() for mapping required values
res = test_str.format(*test_dict.values())

# printing result
print("String after unpacking dictionary : " + str(res))

Output

The original string is : First value is {} Second is {} Third {}
String after unpacking dictionary : First value is Gfg Second is is Third Best

Time Complexity: O(n)
Auxiliary Space: O(n)

Method 2 : Using f-string interpolation and dictionary comprehension.

Step-by-step approach:

• Initialize the string with curly braces for the keys that will be replaced by values from the dictionary.
• Initialize the dictionary with keys as integers and values as strings.
• Use dictionary comprehension to create a new dictionary with keys as strings and values as the corresponding values from the original dictionary.
• Use f-string interpolation to replace the keys in the string with the values from the new dictionary.
• Print the result.

Below is the implementation of the above approach:

Python3

# Python3 code to demonstrate working of
# Unpacking Integer Keys in Strings
# Using f-string interpolation and dictionary comprehension

# initializing string
test_str = "First value is {first} Second is {second} Third is {third}"

# printing original string
print("The original string is : " + str(test_str))

# initializing dictionary
test_dict = {3 : "Gfg", 4 : "is", 9 : "Best"}

# creating new dictionary with keys as strings
new_dict = {"first": test_dict[3], "second": test_dict[4], "third": test_dict[9]}

# using f-string interpolation to replace keys with values
res = test_str.format(**new_dict)

# printing result
print("String after unpacking dictionary : " + str(res))

Output

The original string is : First value is {first} Second is {second} Third is {third}
String after unpacking dictionary : First value is Gfg Second is is Third is Best

Time complexity: O(1), as the dictionary keys are hardcoded and the format string is fixed.
Auxiliary space: O(1), as the size of the dictionaries and strings used is constant