The most common and efficient way to get a key with maximum value in a Python dictionary is to use the max() function with key=dict.get() argument. This method is helpful when you have numeric values in the dictionary.

dict = {"A": 21, "B": 10, "C": 19}

max_key = max(dict, key=dict.get)

print(max_key)  

# Output: A

In this code, key A has a maximum value of 21, which is why it is in the output. We only print the key of that max value. You can also print both the key and the value, depending on your requirements.

It is the cleanest and fastest O(n) Pythonic approach.

Empty dictionary

This happens often when your input dictionary is empty, and you apply the max() function to it. If you are not handling this scenario well, it will throw a ValueError.

empty_dict = {}

max_key = max(empty_dict, key=empty_dict.get)

# ❌ ValueError: max() arg is an empty sequence

To fix the ValueError: max() arg is an empty sequence error, pass default=None to the max() function.

empty_dict = {}

max_key = max(empty_dict, key=empty_dict.get, default=None)

print(max_key)

# Output: None

Multiple keys with the same maximum value

If there is a scenario where there are multiple keys with the same maximum value in a dictionary, the max() function will return the first encountered key.

dict = {"A": 10, "B": 25, "C": 25}

print(max(dict, key=dict.get))

# B (first with value 25)

But what if you want all the keys with maximum values? In that case, you need to use a list comprehension to get the list of keys.

dict = {"A": 10, "B": 25, "C": 25}

max_val = max(dict.values())

max_keys = [k for k, v in dict.items() if v == max_val]

print(max_keys)

# Output: ['B', 'C']

Uncomparable values

What if there is a dictionary with different value types? For example, the first key has an integer value, the second key has a string value, and the third key has a boolean value.

If you apply the max() function on that, it will return TypeError: ‘>’ not supported between instances of ‘str’ and ‘int’ because it cannot compare those values. After all, they are not of the same type.

dict = {"A": 10, "B": "hello", "C": False}

max_keys = max(dict.values())

print(max_keys)

# TypeError: '>' not supported between instances of 'str' and 'int'

Alternate approaches

Approach 1: Using operator.itemgetter()

What if your dictionary is large and contains lots of key-value pairs? In that case, finding the maximum value becomes a lengthy process. That is why you should use the operator.itemgetter() method.

# Large dictionary with 10,000 key-value pairs
# Keys: "key_0", "key_1", ..., "key_9999"
# Values: Random integers between 1 and 1,000,000

import random
from operator import itemgetter

large_dict = {f"key_{i}": random.randint(1, 1_000_000) for i in range(10_000)}

max_key, max_val = max(large_dict.items(), key=itemgetter(1))

print("Max key:", max_key)
# Output: Max key: key_4520

print("Max value:", max_val)
# Output: Max value: 999955

In this code, we used the random module to generate large key-value pairs and find the maximum value.

Approach 2: Using sorted()

What if your task involves sorting the values and then finding the maximum? That’s where you should use the built-in sorted() function.

dict = {"A": 10, "B": 25, "C": 17}

max_key = sorted(dict.items(), key=lambda x: x[1])[-1][0]

print(max_key)

# Output: B

It gives you both sorted data and the max key.

Approach 3: Using a manual loop

The for loop provides complete control over the dictionary, and we can maintain full transparency into the data to find the maximum value. It is not memory-efficient, but yes, it works well with any data.

dict = {"A": 10, "B": 25, "C": 17}

max_key = None
max_value = float("-inf")

for key, value in dict.items():
    if value > max_value:
        max_value = value
        max_key = key

print(max_key)

# Output: B

That’s all!