How to Find the Longest String in a Python Dictionary?

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You’ll never guess the most concise way to solve this problem… 🦄

Coding Challenge

💬 Challenge: Given a dictionary with string keys. Get the string key with the maximum number of characters, i.e., the longest string.

A variant of this problem is to get the length of the longest string — I’ll give you a quick and easy solution for this too. But first, let’s look at an example next, shall we?

Say, you have a dictionary with string keys:

d = {'alice': 18,
     'bob': 23,
     'carl': 35,
     'david': 42}

Desired Output: There are two variants of this challenge.

  1. Get the longest string, i.e., 'alice' or 'david'.
  2. Get the length of the longest string, i.e., 5.

Let’s learn the most Pythonic way to solve this challenge next!

Method 1: Get the Longest String in Dict Keys

To get the longest string key of a dictionary, call max(dict, key=len). You pass the dictionary as a first argument. Python will automatically retrieve the keys from the dictionary and ignore the dictionary values. Then pass the key=len as a second argument to compare the length of the strings and avoid the standard lexicographical string comparison.

Here’s the example:

d = {'alice': 18,
     'bob': 23,
     'carl': 35,
     'david': 42}

print(max(d, key=len))
# alice

💡 The key argument of the max() function allows you to redefine what “maximum” means. In our example, maximum means “longest” string and not “lexicographically largest” string.

Without it, the max() function on a string list would return the lexicographically maximum string, i.e., the one that comes last in the alphabet:

>>> max(['aaaaaaaa', 'z'])
'z'

You can learn more about the key argument of the max() function in our detailed blog tutorial.

👉 Recommended Tutorial: Get Key with Maximum Value in a Python Dictionary

Method 2: Get the Length of the Longest String in Dict Keys

To get the length of the longest string of a dictionary, first find the longest string using max(dict, key=len) and pass the resulting string in the len() function.

Here’s the example:

d = {'alice': 18,
     'bob': 23,
     'carl': 35,
     'david': 42}

print(len(max(d, key=len)))
# 5

Method 3: Get the Longest String From Dict Values

To get the longest string from all dictionary values, call max(dict.values(), key=len). You pass the dictionary values as a first argument. Then pass the key=len as a second argument to compare the length of the strings and avoid the standard lexicographical string comparison.

Here’s the example:

d = {1: 'a', 2: 'aaa', 3:'aa'}
print(max(d.values(), key=len))
# aaa

Method 4: Brute-Force Pure Python

When I was first starting out, I was always looking for the solution that I understood most. I don’t recommend the following solution, it’s super long—but at least it’s simple to understand and you should only include code in your projects that you understand.

You can find the longest string from the dictionary keys by manually comparing all strings in a for loop, keeping track of the maximum by using the len() function and the greater than > operator.

d = {'aaa':1, 'aaaa':2, 'a':3}

longest = ''
for s in d.keys():
    if len(s) > len(longest):
        longest = s

print('The longest string is: ', longest)
# The longest string is:  aaaa

This code snippet is probably most understandable by coders coming from other programming languages such as C++ or Java. However, a skilled Python coder would never write something like this!

👉 Recommended Tutorial: What is the Most Profitable Programming Language?

Programming Humor

💡 Programming is 10% science, 20% ingenuity, and 70% getting the ingenuity to work with the science.

~~~

  • Question: Why do Java programmers wear glasses?
  • Answer: Because they cannot C# …!

Feel free to check out our blog article with more coding jokes. 😉

👉 Related Tutorial: How to Get the Shortest String From a Python Dictionary?