How Can I Find a Dictionary Key Based on its Value in Python?

Retrieving Dictionary Keys Based on Value

When dealing with dictionaries in Python, it is often necessary to locate the key associated with a given value. This scenario arises when you need to find the name of a person based on their age, as in the following example:

dictionary = {'george': 16, 'amber': 19}
search_age = input("Provide age: ")  # Replace raw_input with input in Python 3

However, the provided code encounters a KeyError because it attempts to directly access the value without first verifying its existence. To rectify this, we employ a more robust approach using the following steps:

1. Separate the Dictionary's Values: We create a list containing all the values from the dictionary: values_list = list(dictionary.values())
2. Find the Value's Position: We determine the position of the searched value in the values_list using value_index = values_list.index(search_age)
3. Retrieve the Matching Key: Using the value's position, we obtain the corresponding key from the dictionary's keys: name = list(dictionary.keys())[value_index]
4. Print the Result: We display the retrieved name: print(name)

Consequently, our code now executes successfully:

mydict = {'george': 16, 'amber': 19}
search_age = input("Provide age: ")
values_list = list(mydict.values())
if search_age in values_list:
    value_index = values_list.index(search_age)
    name = list(mydict.keys())[value_index]
    print(name)
else:
    print("Age not found.")

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