The Most Pythonic Way to Join a List in Reverse Order

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The most efficient method to join a list of Python strings in reverse order is to use the Python code ''.join(l[::-1]). First, reverse the list l using slicing with a negative step size l[::-1]. Second, glue together the strings in the list using the join(...) method on the empty string ''.

The Most Pythonic Way to Join a List in Reverse Order

Problem: Given a list of strings. How to join the strings in reverse order?

Example: You want to join the following list

l = ['n', 'o', 'h', 't', 'y', 'p']

to obtain the joined string in reverse order


Let’s get a short overview on how to accomplish this.

Solution Overview: You can try the three methods in our interactive Python shell.

Next, we’ll dive into each method separately.

Method 1: Join + Slicing

The first and most Pythonic method to reverse and join a list of strings is to use slicing with a negative step size.

You can slice any list in Python using the notation list[start:stop:step] to create a sublist starting with index start, ending right before index stop, and using the given step size—which can also be negative to slice from right to left. If you need a refresher on slicing, check out our detailed Finxter blog tutorial or our focused book “Coffee Break Python Slicing”.

Here’s the first method to reverse a list of strings and join the elements together:

l = ['n', 'o', 'h', 't', 'y', 'p']

# Method 1
# python

The string.join(iterable) method joins the string elements in the iterable to a new string by using the string on which it is called as a delimiter.

You can call this method on each list object in Python. Here’s the syntax:


iterableThe elements to be concatenated.

Related articles:

Method 2: Join + reversed()

The second method is also quite Pythonic: using the reversed() built-in function rather than slicing with a negative step size. I’d say that beginners generally prefer this method because it’s more readable to them—while expert coders prefer slicing because it’s more concise and slightly more efficient.

l = ['n', 'o', 'h', 't', 'y', 'p']
# python

The join method glues together all strings in the list—in reversed order!

Method 3: Simple Loop

The third method is the least Pythonic one: using a loop where it’s not really needed. Anyways, especially coders coming from other programming languages like Java or C++ will often use this approach.

l = ['n', 'o', 'h', 't', 'y', 'p']

s = ''
for x in reversed(l):
    s += x
# python

However, there are several disadvantages. Can you see them?

  • The code is less concise.
  • The code is less efficient because of the repeated string concatenation. Each loop execution causes the creation of a new string, which is highly inefficient.
  • The code requires the definition of two new variables x and s and introduces a higher level of complexity.

You can see this in our interactive memory visualizer:

Exercise: click “Next” to see the memory objects used in this code snippet!

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Where to Go From Here?

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