What is Indentation Error? How to Solve Indentation Error in Python?

As an interpreted, high-level and general-purpose programming language, Python is increasingly garnering accolades as the programming world’s most promising, leading and emerging platforms. Python is nothing without its ingenious design philosophy.

A key characteristic is an emphasis drawn to the notable use of significant indentation to enhance code-readability. The illustration highlighted below succinctly outlines the bulwarks of Python’s design philosophy as twenty aphorisms, alluded by Tim Peters, long-term Pythoneer, who eventually became one of Python’s most prolific and tenacious core developers.

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A Brief Introduction to Python

Before we delve into the specific technicalities underlying the indentation error in Python, it is imperative that we get acquainted with the fundamentals of Python and the need for indentation. Doing so will not only help you gain a better appreciation of the error itself but offer an insight into the advantages that programmers gain by effectively choosing to resolve the same. 

The inception of Python as a multi-paradigm programming language can be traced back to the year 1991. Since then, programmers have continually adapted Python’s core wireframe to suit a range of user-specific needs, such as data science and web and mobile development. 

Now, we all know that attempting to comprehend illegible handwriting is painstakingly tricky and often infuriating. Similarly, an unreadable and unstructured code is plain and simple, unacceptable in the programming world. This is where the notion of PEP or Python Enhancement Proposal comes to the programmer’s rescue. PEP to the Python Community is akin to a shared Google Doc for the general populace.

It is a continually updated descriptive mandate that keeps the Python programming community comprehensively informed of features and updates to improve code readability. Written by Guido van Rossum, Barry Warsaw and Nick Coghlan in 2001, the PEP 8 is referred to as Python’s style code. 

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What is Indentation?

It is primarily known that Python is a procedural language, and therefore, an indentation in Python is used to segregate a singular code into identifiable groups of functionally similar statements. The majority of the programming languages, including C, C++ and JAVA, employ curly braces ‘{}’ to define a block of code. Python marks a deviation from this design and prefers the use of indentation. 

Syntax of Indentation

According to the conventions outlined by PEP 8 whitespace ethics, every new iteration (i.e., a block of code) should start with an indentation, and the ending of the code should be the first-line that is not indented. The common practice to execute an indentation is four white spaces or a single tab character, with spaces being largely preferred over tabs. The mixing of spaces and tabs is forbidden.  

Causes of Indentation Error in Python

The ‘Indentation Error: Expected an indented block’ does not discriminate between users. Whether you are a novice at Python programming or an experienced software developer, this is bound to happen at some point in time. In Python, since all the code you type is arranged via correct whitespaces, if at any instance in the code, you have an incorrect indentation, the overall code with not run, and the interpreter will return an error function. To know exactly what to keep an eye out for, the following lists some of the common causes of an indentation error in Python:

  • The simultaneous use of tabs and space while coding. It can be argued that in theory, both tabs and spaces serve the same purpose, but let us consider this from the perspective of the interpreter. If white spaces and tabs are used inconsistently and interchangeably, it creates ambiguity. This will result in the interpreter getting confused between which alteration to use and eventually returning an indentation error in Python.
  • You have unintentionally placed an indentation in the wrong place or there is an absence of tabs or white spaces between lines of code. Since Python adheres to strict guidelines to arrange written codes, an indentation in the wrong place will inevitably return an error. For example, the first line of Python should not be indented. 
  • Occasionally, while finishing an overdue, exceptionally long program, you might unknowingly miss out on indenting compound statement functions such as for, while and if. This will again lead to an indentation error. This is the most basic need for indentation when using Python and needs to be rigorously practiced to master.
  • If you have forgotten to use indentation when working with user-defined functions or different classes, an error is likely to pop up. 

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How to Solve an Indentation Error in Python?

  • Check for wrong white spaces or tabs. Unfortunately, there is no quick fix to an indentation error. Since the code is yours, the fact remains that you will have to individually assess each line to identify erroneous instances. However, since lines of code are arranged in blocks, the process is relatively simple. For example, if you have used the ‘if’ statement in a particular line, you can cross-check if you have remembered to indent the following line.
  • Be certain that the indentation for a specific block remains the same throughout the code, even if a new block is introduced in the middle. Check for inconsistencies in the indentation.

If the above manual solutions did not work for you, and you are having a hard time figuring out where you missed the indentation, then follow these steps:

  • Go to your code editor settings and enable the option that seeks to display tabs and whitespaces. With this feature enabled, you will see single small dots, where each dot represents a tab/white space. If you notice a dot is missing where it shouldn’t be, then that line probably has an indentation error.
  • Use the Python interpreter built-in Indent Guide. Arguably, this method is highly inefficient for several code lines. However, since it takes you through each line and shows you exactly where your error lies, it is the surest way to find and fix all errors. 

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Benefits of Indentation

Readability and consistency are essential for any good code. Following the PEP 8 whitespace, ethics should thus be non-negotiable. It logically substantiates your code, thereby contributing to a more pleasant coding experience. Additionally, if you follow this stylistic guideline where readability is your de facto, people who are unknown to you, but are interested in your work, will understand your code with ease. 

Disadvantages of Indentation

  • If the code is large and the indentation is corrupted, it can be tedious to fix indentation errors. This is usually the case when a code is copying from an online source, Word document or PDF file. 
  • Popular programming languages typically use braces for indentation. For programmers just beginning to use Python, adjusting to the idea of using whitespaces for indentation can be difficult. 

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Summing Up

All that lies between you and a well-written code is indentation, and all that lies between you, your well-written code and its seamless execution is an indentation error. Now, all humans make mistakes. All programmers are humans. Therefore, all programmers make mistakes. But an indentation error can easily be resolved. All you need to do is breathe and take your space. 

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