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 ''.
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
python
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
print(''.join(l[::-1]))
# pythonThe 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:
string.join(iterable)
| Argument | Description |
|---|---|
iterable | The elements to be concatenated. |
Related articles:
- Python Join List [Ultimate Guide]
- Python Slicing [Ultimate Guide]
- How to Reverse a Python List
- The Ultimate Guide to Python Lists
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']
print(''.join(reversed(l)))
# pythonThe 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
print(s)
# 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
xandsand 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!
Related articles:
Where to Go From Here?
Enough theory. Let’s get some practice!
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