Python Text Read List Index Out of Range
Surprise, surprise! We're back with another article on a Python exception. Of course, this fourth dimension we're moving away from the SyntaxError and into a more specialized error, the IndexError, which is accompanied by various error messages. The error message we'll be talking about today reads: IndexError: cord alphabetize out of range.
In case you're short on time, this IndexError arises when a string is accessed using an invalid index. For example, the cord "VirtualFlat" has eleven characters. If a user were to try to access a character beyond this limit—say "VirtualFlat"[15] —an IndexError would arise.
In the remainder of this article, nosotros'll expect at this IndexError more than deeply. For instance, nosotros'll take a look at the IndexError broadly. Then, we'll hone in on the specific message. After that, nosotros'll wrap things upward with some potential solutions and offer up an opportunity to share your code if you're withal having trouble.
Table of Contents
What Is an IndexError?
According to Python documentation, an IndexError is raised whenever "a sequence subscript is out of range." Of course, what does that really mean?
To break downwards this definition, we need to sympathize a few terms. Get-go, a sequence is a list-like object where items are stored in club; think lists, strings, and tuples. In this context, a subscript is then another proper noun for an item's index.
In Python, for an index to be out of range, information technology must not exist. For example, if we had a string like "VirtualFlat", a valid index would be whatsoever value less than the length of the cord and greater than or equal to the negative length of the string:
# Declare some alphabetize brand = "VirtualFlat" is_valid_index = -len(make) <= index < len(brand)
As we can run across, the range of indices is actually asymmetric. This is because negative indexing starts from negative ane—as opposed to zero during regular indexing.
On a side annotation, I probably should take represented the range mathematically, but I struggled to come upwards with a syntax where the length operator wasn't the exact same operator as absolute value (i.e. |x|). Besides, the lack of symmetry made the expression clunky either mode. I would accept preferred something similar |index| < |brand|, but information technology ends up being -|brand| <= index < |brand|. Perhaps interval notation would be a bit cleaner: [-|brand|, |brand|).
At any rate, all this means is that there are valid and invalid indices. For example, the following lawmaking snippets volition result in an IndexError:
brand = "VirtualFlat" make[17] # out of range brand[-12] # out of range
Of course, this aforementioned idea applies to any sequence type. For example, nosotros could encounter this same error turn upwards for any of the post-obit sequences:
nums = [1, 4, 5] nums[7] # IndexError: list alphabetize out of range
nums = (i, 4, 5) nums[7] # IndexError: tuple alphabetize out of range
nums = range(5) nums[seven] # IndexError: range object alphabetize out of range
In the next section, we'll take a look at this mistake in the context of its fault bulletin.
What Does This IndexError Message Mean?
Up to this signal, nosotros've talked about the IndexError broadly, but the mistake message we're dealing with gives usa a bit more information: IndexError: string index out of range.
Here, nosotros tin can encounter that we're not dealing with a list or tuple. Instead, we're working with a string. Every bit a result, our original case nevertheless holds:
brand = "VirtualFlat" make[17] # out of range make[-12] # out of range
That said, there are other ways we could become this fault message to arise. For example, the Formatter class
of string can throw the same fault when using the get_value() method.
In fact, there are probably thousands of libraries that could throw this error, so it'due south tough for me to assume your situation. As a result, in the next section, we'll take a wait at the simple example and try to come up with some general problem solving strategies.
How to Set up This IndexError?
At present that nosotros know nosotros have some sort of indexing issue with our string, it'due south just a matter of finding the root cause.
Like the original scenario we explores, it'south possible that we have some hardcoded value that is breaching the range of our cord:
brand = "VirtualFlat" brand[17] # out of range
In this case, we'll probably want to generate a abiding from this index and give it a practiced name. After all, maintaining a magic number is usually a bad thought:
make = "VirtualFlat" LAST_CHAR = 10 make[LAST_CHAR]
Having solved our magic number issue, I'd contend that there'southward an even better solution: nosotros should compute the last character programatically. Of form, if nosotros're not conscientious, we could find ourselves with however another IndexError:
make = "VirtualFlat" brand[len(brand)] # out of range, over again
To get the last graphic symbol, we'll demand to subtract one from the length:
brand = "VirtualFlat" brand[len(brand) - ane]
That said, if y'all've read my guide to getting the last particular of a list, you know there'southward an even cleaner solution. Of class, we're non here to get the last character of a string; we're trying to conceptualize different means in which this mistake could ascend.
For case, we might be doing something a bit more complicated like looping over a string:
brand = "VirtualFlat" i = 0 while i <= len(make): if i % two == 0: print(brand[i]) # sometimes out of range
Here, we'll notice that the loop condition always takes the index one step too far. As a upshot, nosotros'll need to correct it:
brand = "VirtualFlat" i = 0 while i < len(brand): if i % 2 == 0: print(brand[i]) # sometimes out of range
Or even ameliorate, we tin can take advantage of the for loop:
make = "VirtualFlat" for i, c in enumerate(make): if i % ii == 0: print(c) # sometimes out of range
Of course, this doesn't even begin to scratch the realm of possibility for this error. As a result, in the next department, we'll take a look at getting yous some extra help—if you need information technology!
Need Aid Fixing This IndexError?
Every bit someone who has been relieved of their teaching duties for a little while, I figured I'd kickoff sharing my time with the folks of the net. In other words, if y'all find this article helpful merely didn't quite give you lot what you needed, consider sharing your code snippet with me on Twitter.
To do that, you're welcome to utilise the #RenegadePython hashtag. Typically, I apply that for Python challenges, simply I figured I'd open up it up for general Python Q&A. Here's a sample tweet to get you started:
At any rate, that's all I've got for today. If y'all liked this commodity, I'd appreciate it if you fabricated your way over to my listing of ways to grow the site. In that location, you'll find links to my newsletter, YouTube aqueduct, and Patreon.
Likewise, here are a few related articles for your perusal:
- Rock Newspaper Pair of scissors Using Modular Arithmetic
- How to Get the Last Item of a List in Python
Finally, here are a few additional Python resource on Amazon (ad):
Otherwise, thank you for stopping by and enjoy the rest of your day!
Python Text Read List Index Out of Range
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