How to Find the Longest String in a Python Set?

Use Python’s built-in `max()` function with the `key` argument to find the longest string in a set. Call `max(my_set, key=len)` to return the longest string in the set using the built-in `len()` function to determine the weight of each string—the longest string has maximum length.

👉 Recommended Tutorial: How to Find the Longest String in a Python List?

Problem Formulation

Given a Python set of strings. Find the string with the maximum number of characters—the longest string in the set.

Here are a few example set of strings and the desired output:

```# {'Alice', 'Bob', 'Pete'}   ---->   'Alice'
# {'aaa', 'aaaa', 'aa'}      ---->   'aaaa'
# {''}                       ---->   ''
# {}                         ---->   ''```

Method 1: max() Function with Key Argument Set to len()

Use Python’s built-in `max()` function with a key argument to find the longest string in a set like so: `max(s, key=len)`. This returns the longest string in the set `s` using the built-in `len()` function to determine the weight of each string—the longest string will be the maximum.

Here’s the code definition of the `get_max_str()` function that takes a set of strings as input and returns the longest string in the list or a `ValueError` if the set is empty.

```def get_max_str(my_set):
return max(my_set, key=len)```

Here’s the output we obtain when running our desired examples:

```print(get_max_str({'Alice', 'Bob', 'Pete'}))
# 'Alice'

print(get_max_str({'aaa', 'aaaa', 'aa'}))
# 'aaaa'

print(get_max_str({''}))
# ''```

If you pass an empty set, Python will raise a `ValueError: max() arg is an empty sequence` because you cannot pass an empty iterable into the `max()` function.

```print(get_max_str({}))
# ValueError: max() arg is an empty sequence```

Method 2: Handling Empty Sets

If you want to return an alternative value in case the set is empty, you can modify the `get_max_str()` function to include a second optional argument:

```def get_max_str(my_set, fallback=''):
return max(my_set, key=len) if my_set else fallback

print(get_max_str({}))
# ''

print(get_max_str({}, fallback='EMPTY!!!!!!'))
# EMPTY!!!!!!```

Method 3: Not-So-Pythonic with For Loop

A less Pythonic but, for beginner coders, more readable version is the following loop-based solution:

```def get_max_str(my_set, fallback=''):
if not my_set:
return fallback

max_str = ''   # set is not empty

for x in my_set:
if len(x) > len(max_str):
max_str = x

return max_str

print(get_max_str({'Alice', 'Bob', 'Pete'}))
# 'Alice'

print(get_max_str({'aaa', 'aaaa', 'aa'}))
# 'aaaa'

print(get_max_str({''}))
# ''

print(get_max_str({}, fallback='EMPTY!!!!!!'))
# EMPTY!!!!!!```

Method 4: Python Max Length of String in Set

To find the maximum length of a string in a given set, use the `max(my_set, key=len)` function to obtain the string with the maximum length and then pass this max string into the `len()` function to obtain the number of characters of the max string.

``len(max(my_set, key=len))``

Here’s a more detailed example:

```def get_max_length(my_set):
return len(max(my_set, key=len))

print(get_max_length({'Alice', 'Bob', 'Pete'}))
# 5

print(get_max_length({'aaa', 'aaaa', 'aa'}))
# 4

print(get_max_length({''}))
# 0

print(get_max_length({}))
# ValueError: max() arg is an empty sequence
```