Indexerror: list index out of range: How to solve it effectively in Python

If you are app developers, you should not miss this article. Because in this article, we will bring to you a programming language called Python. Python is a programming language that enables you to work faster and easier with systems. Meanwhile, one of the most common examples of runtime problems in Python is IndexErrors. They’re triggered when you try to access an index value that doesn’t exist in a Python list. Index mistakes are typically simple to fix. Therefore, all you have to do now is debug a little. So in this blog, ArrowHiTech will discuss Indexerror: list index out of range python for loop. Additionally, we’ll go through How to solve it effectively in Python. Let’s explore now.

What is indexerror: list index out of range Python for loop

The best place to start, like always, is to read and break down the error message:

indexerror: list index out of range Python for loop

This error message indicates that we are trying to retrieve a value within an array without an index position.

In Python, index numbers begin at zero. Here’s an example of a Python array

programming_languages = [“Java”, “Python”, “C++”]

There are three values in this array. The index value of the first list element- Java is 0. After that, each value has an index number that is one higher than the previous one. Python’s index value, for example, is 1.

An error will give if we try to access an item at index position 3. The index value 2 is assigned to the last item in our array.

How to solve Indexerror: list index out of range Python for loop effectively?

The “list index out of range” problem usually occurs in one of two scenarios:

  • When you’re trying to iterate through a list and forget that lists start at zero.
  • When you forgot to iterate through a list using range().

So now let’s take a look at both of the following scenarios.

Lists Are Indexed From Zero

To the Python shell, the following program prints all the values in a list called “programming languages”:

programming_languages = [“Java”, “Python”, “C++”]

count = 0 

while count <= len(programming_languages):

print(programming_languages[count])

count += 1

Firstly, we started by declaring two variables. The list of languages we wish to print to the console is stored in the variable “programming languages.” We utilize the variable “count” to keep track of how many values have been printed to the console.

Following that, we’ve declared a while loop. The value from the “programming languages” variable is printed at the index position contained in “count” in this loop. Then it increments the “count” variable by one. This loop is repeated until the value of “count” equals or exceeds the length of the “programming languages” list.

Let’s see if we can run our code:

Java

Python

C++

Traceback (most recent call last):

  File “main.py”, line 5, in <module>

print(programming_languages[count])

Indexerror: list index out of range Python for loop

Our list’s values are printed to the console. However there is an error. Therefore, our loop continues until the value of “count” no longer equals or is less than the length of “programming languages” . So it means that the final iteration will check for the following:

programming_languages[3]

There is no such thing as this value. An IndexError is as a result of this. We may overcome this problem by changing our operator from <= to <. Therefore, this ensures that our list will only iterate until the value of “count” equals or exceeds the length of “programming languages.” So let’s make this change:

programming_languages = [“Java”, “Python”, “C++”]

count = 0 

while count < len(programming_languages):

print(programming_languages[count])

count += 1

The following is the output of our code:

Java

Python

C++

Finally, we’ve found out how to fix the problem! Our loop isn’t trying to output programming languages[3] any longer. Because 3 is not less than the length of “programming languages,” it will stop when the value of “count” equals 3.

Forget to Use range()

It’s easy to forget to include a range() statement when iterating over a list of numbers. If you try to access anything in this list, you might get an error.

Consider the code below:

ages = [9, 10, 9]

for age in ages:

print(ages[age])

All of the values in the “ages” array should be printed out with this code. The ages of pupils in a middle school class are shown in this array.

Let’s see what occurs if we execute our program:

Traceback (most recent call last):

  File “main.py”, line 4, in <module>

print(ages[age])

Indexerror: list index out of range Python for loop

An error has occurred. To understand what has happened, we’ll add a print statement to our loop to view the value of “age” in each iteration:

ages = [9, 10, 9]

for age in ages:

print(age)

print(ages[age])

The following is the output of our code:

9

Traceback (most recent call last):

  File “main.py”, line 5, in <module>

print(ages[age])

Indexerror: list index out of range Python for loop

The console displays the first age, which is 9. On the other hand, the value of “age,” is derived from “ages.” So it’s not an index number. Therefore, we’re trying to retrieve an age by its index number on the “print(ages[age])” line of code.

When we run our code, it looks for the following: ages[9]. In the first iteration, the value of “age” is 9. As a result, this value does not appear in our “ages” list.

We may use a range() function to loop through our list of ages to solve this problem:

ages = [9, 10, 9]

for age in range(0, len(ages)):

print(ages[age])

So now let’s run our code one more time;

Indexerror: list index out of range:

The “ages” array’s values are all reported to the console. The range() statement generates a list of numbers that are within a specific range. The range [0, 1, 2] is produced in this example. These numbers can then be used to find values in “ages” based on their index number.

Besides that, we could also use a “for…in” loop without needing indexing:

ages = [9, 10, 9]

for age in ages:

print(age)

This code returns:

Indexerror: list index out of range:

Our code does not attempt to retrieve any values from the “ages” array by index. Instead, our loop iterates through the “ages” array, printing each number to the terminal.

Conclusion

Are you clear about Indexerror: list index out of range Python for loop? In case you want to find out about Python. Then, during the process of working with Python or any programming language, if you are having any difficult issues, let contact us. ArrowHitech has become one of the superior IT outsourcing Vietnam companies. We are experienced professionals in the field of  ECommerce, Web/mobile apps, CMS website development as well as Salesforce and Software Consultant & Development.

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