Python – Find Longest Line/String in File

Coding Challenge

💬 Challenge: How to Find the Longest Line or String From a File in Python?

Given the following text file:

Depending on what exactly you’re looking for, you want to find the longest string word (A) or the longest line (B) in the file.

without
python
we'd all have to
write 
java
code

Let’s dive into both variants next.

Method 1: Find Longest Line in Text File using Python

To find the longest line in a text file using Python, open the file using the open() function and read the file content in a list of lines using file.readlines() function. Then call the max(lines, key=len) function on the list of lines using the length function as a key to find the longest line.

Here’s the code:

with open('my_file.txt', mode='r') as f:
    lines = f.readlines()
    longest_line = max(lines, key=len)
    print('The longest line is:', longest_line)

The output is:

The longest line is: we'd all have to

You may want to check out the following tutorials to help you understand the basics of the features used in this snippet:

• Python open() function
• Read file to list
• Python max() function
• Python len() function

Or why not open all four tutorials and skim them in 1 minute per tutorial? Four minutes well spent! 🦄

Note you can one-linerize this using the following code snippet:

print(max(open('my_file.txt').readlines(), key=len))
# we'd all have to

Method 2: Find Longest String Word in a Text File using Python

A simple and straightforward way to find the longest string word in a text file is to open the file, loop over all lines using file.readlines(), split each line into a list of words using string.split(), loop over this list of words, and keep track of the longest word in a variable.

Here’s the Python snippet that finds the longest word in a text file:

with open('my_file.txt', 'r') as f:
    longest_word = ''
    for line in f.readlines():
        for word in line.split():
            if len(word)>len(longest_word):
                longest_word = word
    print('The longest word in the file is:', longest_word)

Here’s the correct output, i.e., the longest word in the text:

The longest word in the file is: without

Note, you can also one-linerize this using the following approach of combining list comprehension and the max() function:

longest = max([word for line in open('my_file.txt').readlines() for word in line.split()], key=len)

The result is the same:

print('The longest word in the file is:', longest)
# The longest word in the file is: without

In case you’re confused by the one-liner solution, no worries. First have a look at the list comprehension tutorial.

👉 Recommended Tutorial: A Simple Guide to Python’s List Comprehension

Second, you may also want to check out my book on the topic that will make you a one-liner wiz:

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