As a professional in the field, I have found Python to be an interpreted, high-level, and general-purpose programming language that garners accolades as one of the most promising platforms in the programming world. Python’s ingenious design philosophy is essential to its success.

A key characteristic of Python is its emphasis on significant indentation to enhance code readability. The illustration below outlines Python’s design philosophy through twenty aphorisms, as alluded to by Tim Peters, a long-term Pythoneer who eventually became one of Python’s most prolific core developers.

One common issue many encounter is the indentation error in Python. Understanding and mastering Python’s indentation rules is crucial for writing clean and error-free code.

A Brief Introduction to Python

Before we delve into the specific technicalities underlying the indentation error in Python, we must get acquainted with Python’s fundamentals 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. 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 code block. 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 areas being largely preferred over tabs.

As discussed earlier, the leading whitespaces at the start of a line determine the line’s indentation level. To group the statements for a particular code block, you will have to increase the indent level. Similarly, to close the grouping, you will have to reduce the indent level. 

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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:

1. 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.

2. You have unintentionally placed an indentation in the wrong place or an absence of tabs or white spaces between code lines. 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. 

3. 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 practised to master.

4. 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?

1. 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 assess each line to identify erroneous instances individually. 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 sequence, you can cross-check if you have remembered to indent the following line.

2. 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:

3. 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 drop is missing where it shouldn’t be, then that line probably has an indentation error.

4. 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 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

Between a programmer and well-written code lies merely an indentation. Likewise, between me, my well-written code, and its seamless execution looms the possibility of an indentation error in Python. Given that all humans make mistakes, and all programmers are human, it follows that all programmers make mistakes. However, resolving such an indentation error is straightforward. It merely requires taking a breath and claiming your space. 

I trust you will gain valuable insights from working on these Python projects. If you’re eager to stay ahead in the fast-paced world of technological advancements and delve into data science, explore upGrad & IIIT-B’s Executive PG Programme in Data Science. Upskill yourself for the future. 

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