[Tut] Python Join List Range: A Helpful Guide

[Tut] Python Join List Range: A Helpful Guide - Printable Version

+- Sick Gaming (https://www.sickgaming.net)
+-- Forum: Programming (https://www.sickgaming.net/forum-76.html)
+--- Forum: Python (https://www.sickgaming.net/forum-83.html)
+--- Thread: [Tut] Python Join List Range: A Helpful Guide (/thread-95641.html)

[Tut] Python Join List Range: A Helpful Guide - xSicKxBot - 06-12-2020

Python Join List Range: A Helpful Guide

<div>If the search phrase “Python Join List Range” brought you here, you’re having most likely one of the following problems:
<ol>
<li>You don’t know how to <a rel="noreferrer noopener" href="https://blog.finxter.com/concatenate-lists-in-python/" target="_blank">concatenate </a>two <code>range()</code> iterables, or</li>
<li>You want to use <code><a rel="noreferrer noopener" href="https://blog.finxter.com/python-join-list/" target="_blank">.join()</a></code> to create a string from a <code>range()</code> iterable—but it doesn’t work.</li>
</ol>
In any case, by reading this article, I hope that you’ll not only answer your question, you’re also become a slightly better (Python) coder by understanding important nuances in the<a href="https://blog.finxter.com/python-crash-course/" target="_blank" rel="noreferrer noopener"> Python programming language</a>.
But let’s first play with some code and get an overview of the two solutions, shall we?
 <iframe src="https://trinket.io/embed/python/e36ce7dbd8" width="100%" height="356" frameborder="0" marginwidth="0" marginheight="0" allowfullscreen></iframe> 
Exercise: Can you accomplish both objectives in a single line of Python code?
<figure class="wp-block-image size-large is-resized"><img src="https://blog.finxter.com/wp-content/uploads/2020/06/graphic-1024x576.jpg" alt="Python Join List Range" class="wp-image-9484" width="768" height="432" srcset="https://blog.finxter.com/wp-content/uploads/2020/06/graphic-scaled.jpg 1024w, https://blog.finxter.com/wp-content/uploads/2020/06/graphic-300x169.jpg 300w, https://blog.finxter.com/wp-content/uploads/2020/06/graphic-768x432.jpg 768w" sizes="(max-width: 768px) 100vw, 768px" /></figure>
<h2>Concatenate Two range() Iterables</h2>
Problem: How to create a new list by concatenating two <code>range()</code> iterables?
Example: You want to concatenate the following two <code>range()</code> iterables
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">range(1,5) + range(5,10)</pre>
Your expected result is:
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">[1, 2, 3, 4, 5, 6, 7, 8, 9]</pre>
Developing the Solution: The result of the <code>range(start, stop, step)</code> function is an iterable “range” object:
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">>>> range(10)
range(0, 10)
>>> type(range(10))
<class 'range'></pre>
Unfortunately, you cannot simply concatenate two range objects because this would cause a <code>TypeError</code>—the + operator is not defined on two range objects:
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">>>> range(1, 5) + range(5, 10)
Traceback (most recent call last): File "<pyshell#2>", line 1, in <module> range(1, 5) + range(5, 10)
TypeError: unsupported operand type(s) for +: 'range' and 'range'</pre>
Thus, the easiest way to concatenate two range objects is to do the following.
<ul>
<li>Convert both range objects to lists using the <code>list(range(...))</code> function calls.</li>
<li>Use the <a href="https://blog.finxter.com/python-list-concatenation-add-vs-inplace-add-vs-extend/" target="_blank" rel="noreferrer noopener">list concatenation</a> operator <code>+</code> on the resulting objects.</li>
</ul>
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">l = list(range(1, 5)) + list(range(5, 10))
print(l)
# [1, 2, 3, 4, 5, 6, 7, 8, 9]</pre>
There are other ways to <a rel="noreferrer noopener" href="https://blog.finxter.com/concatenate-lists-in-python/" target="_blank">concatenate lists</a>—and a more efficient one is to use the <code><a rel="noreferrer noopener" href="https://docs.python.org/3/library/itertools.html#itertools.chain" target="_blank">itertools.chain()</a></code> function.
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">from itertools import chain
l = chain(range(1, 5), range(5, 10))
print(list(l))
# [1, 2, 3, 4, 5, 6, 7, 8, 9]</pre>
This has the advantage that you work purely on iterables rather than <a rel="noreferrer noopener" href="https://blog.finxter.com/python-lists/" target="_blank">lists</a>. There’s no need to waste computational cycles to create a list object if you need it only to <a rel="noreferrer noopener" href="https://blog.finxter.com/python-list-concatenation-add-vs-inplace-add-vs-extend/" target="_blank">concatenate </a>it to another list object. By avoiding the superfluous list creation, you win in <a rel="noreferrer noopener" href="https://blog.finxter.com/python-cprofile-a-helpful-guide-with-prime-example/" target="_blank">performance </a>(at the costs of adding another <a rel="noreferrer noopener" href="https://blog.finxter.com/the-complete-python-library-guide/" target="_blank">library </a>to your code). 
You can see how the first version creates multiple list objects in memory in the interactive memory visualizer:
 <iframe width="800" height="500" frameborder="0" src="https://pythontutor.com/iframe-embed.html#code=l1%20%3D%20list%28range%281,%205%29%29%20%0Al2%20%3D%20list%28range%285,%2010%29%29%0Al%20%3D%20l1%20%2B%20l2%0Aprint%28l%29&codeDivHeight=400&codeDivWidth=350&cumulative=false&curInstr=3&heapPrimitives=nevernest&origin=opt-frontend.js&py=3&rawInputLstJSON=%5B%5D&textReferences=false"> </iframe> 
Exercise: How many list objects are there in memory after the code terminates?
<h2>Use .join() to Create a String From a range() Iterable</h2>
Problem: Given a range object—which is an iterable of integers—how to join all integers into a new string variable?
Example: You have the following range object:
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">range(10)</pre>
You want the following string:
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">'0123456789'</pre>
Solution: To convert a range object to a string, use the <a rel="noreferrer noopener" href="https://blog.finxter.com/python-join-list/" target="_blank"><code>string.join()</code></a> method and pass the <a href="https://blog.finxter.com/list-comprehension/" target="_blank" rel="noreferrer noopener">generator expression</a> <code>str(x) for x in range(...)</code> to convert each integer to a string value first. This is necessary as the join function expects an iterable of strings and not integers. If you miss this second step, Python will throw a <code>TypeError</code>:
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">print(''.join(range(10))) '''
Traceback (most recent call last): File "C:\Users\xcent\Desktop\code.py", line 2, in <module> print(''.join(range(10)))
TypeError: sequence item 0: expected str instance, int found '''</pre>
So, the correct way is to convert each element to a string using the <a href="https://blog.finxter.com/how-to-use-generator-expressions-in-python-dictionaries/" target="_blank" rel="noreferrer noopener">generator expression</a> <code>str(x) for x in range(...)</code> inside the <code>join(...)</code> argument list. Here’s the correct code that joins together all integers in a range object in the most Pyhtonic way:
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">print(''.join(str(x) for x in range(10))) '0123456789'</pre>
You can use different <a href="https://blog.finxter.com/convert-list-of-tuples-to-string/" target="_blank" rel="noreferrer noopener">delimiter </a>strings if you need to:
<pre class="EnlighterJSRAW" data-enlighter-language="generic" data-enlighter-theme="" data-enlighter-highlight="" data-enlighter-linenumbers="" data-enlighter-lineoffset="" data-enlighter-title="" data-enlighter-group="">print('-'.join(str(x) for x in range(10))) '0-1-2-3-4-5-6-7-8-9'</pre>
Related articles:
<ul>
<li><a href="https://blog.finxter.com/python-join-list/" target="_blank" rel="noreferrer noopener">Python Lists [Ultimate Guide]</a></li>
<li><a href="https://blog.finxter.com/python-join-list/" target="_blank" rel="noreferrer noopener">Python Join [Ultimate Guide]</a></li>
<li><a href="https://blog.finxter.com/which-is-faster-list-comprehension-or-map-function-in-python/" target="_blank" rel="noreferrer noopener">Python Generator Expressions and List Comprehension</a></li>
</ul>
<h2>Where to Go From Here?</h2>
Enough theory, let’s get some practice!
To become successful in coding, you need to get out there and solve real problems for real people. That’s how you can become a six-figure earner easily. And that’s how you polish the skills you really need in practice. After all, what’s the use of learning theory that nobody ever needs?
Practice projects is how you sharpen your saw in coding!
Do you want to become a code master by focusing on practical code projects that actually earn you money and solve problems for people?
Then become a Python freelance developer! It’s the best way of approaching the task of improving your Python skills—even if you are a complete beginner.
Join my free webinar <a rel="noreferrer noopener" href="https://blog.finxter.com/webinar-freelancer/" target="_blank">“How to Build Your High-Income Skill Python”</a> and watch how I grew my coding business online and how you can, too—from the comfort of your own home.
<a href="https://blog.finxter.com/webinar-freelancer/" target="_blank" rel="noreferrer noopener">Join the free webinar now!</a>
</div>

https://www.sickgaming.net/blog/2020/06/10/python-join-list-range-a-helpful-guide/