Adventures in Machine Learning

The Power of Whitespace in Python Programming: Best Practices and Pitfalls

Python Statements and Line Continuation: A Comprehensive Guide

1) Sequential Execution of Statements

Python, a versatile programming language, executes statements sequentially, meaning each line of code runs in the order it appears in the script or interactive session. This allows programmers to design code that performs operations in a specific sequence. Consider the following code:

number1 = 5
number2 = 10
sum = number1 + number2

Here, the statements are executed sequentially: First, variables ‘number1’ and ‘number2’ are assigned values; then, the sum is computed and stored in ‘sum’; finally, the result is printed using the ‘print()’ function.

2) REPL Session and Script File Execution

Python supports two execution modes: REPL (Read-Eval-Print Loop) and script files.

  • In a REPL session, you enter Python code line by line, getting immediate results. This is useful for experimenting with code snippets or testing small code parts.
  • A script file contains a sequence of Python statements executed as a single unit. To execute a script file, you can use the command-line interface or an IDE like PyCharm or Visual Studio Code.

3) One Statement per Line

It is a common and recommended practice to write one statement per line in Python code, making it more readable and easier to understand. For instance:

number1 = 5
number2 = 10
sum = number1 + number2

However, long statements might not fit on a single line. In such cases, we can use line continuation techniques to split the statement.

4) Implicit Line Continuation

Python’s implicit line continuation feature allows statements to span multiple lines without explicit characters. This is achieved by enclosing the statement in parentheses, brackets, or curly braces. For example:

numbers = [1, 2, 3,
           4, 5, 6]

The list ‘numbers’ spans multiple lines, but because it is enclosed in square brackets, Python treats it as a single statement.

5) Usage of Grouping Parentheses

Another line continuation method is using grouping parentheses. A statement is enclosed in parentheses and continued on the next line. For example:

sum = (number1
       + number2
       + number3)

Note that the closing parentheses must be on the same line as the opening ones to avoid syntax errors.

6) Multiple Parentheses, Brackets, or Curly Braces Usage

Python allows using multiple parentheses, brackets, or curly braces to split statements across lines. For example:

result = func1((arg1, arg2, arg3),
               [item1, item2, item3],
               {key1: value1, key2: value2})

This technique splits complex statements into smaller, manageable parts, improving readability and organization.

3) Multiple Statements Per Line

Writing multiple statements on a single line is heavily discouraged in Python. Although technically allowed, it is considered unPythonic. Python prioritizes readability over conciseness. Multiple statements per line contradict this ethos, making the code harder to read and follow, especially for beginners. It can also lead to unexpected behavior and bugs. For example:

x = 5; y = 10; z = x + y;

This code assigns values to ‘x’ and ‘y’, computes the sum, and prints the result. However, its readability is compromised. It’s better to write it with one statement per line, as follows:

x = 5
y = 10
z = x + y

Using one statement per line makes the code more organized and easier to understand.

4) Comments

Comments in Python are textual annotations inserted into the code to explain its purpose and functionality. They are meant for other programmers, not the computer, to enhance code understanding and make it easier to maintain, troubleshoot, and modify.

The Importance of Comments

Comments enhance the readability and maintainability of Python code. They provide context for other programmers, making it easier to grasp the purpose of a specific section of code. Effective comments save hours of debugging later, particularly in large projects.

Single-line Comments

Single-line comments are denoted by a hash symbol (#). They are used to provide brief explanations for a specific line of code. For example:

# This is a single-line comment in Python
print("Hello, World!")  # Print the message "Hello, World!"

The first line is a single-line comment that doesn’t affect code execution. It provides additional information about what the code does.

Multi-line Comments

Multi-line comments in Python are denoted by triple quotes (“”” or ”’), also known as docstrings. They are more versatile, offering detailed explanations for code sections, functions, or entire modules.

For example:

This is an example of a multi-line comment in Python.
It can span multiple lines and is used to provide a detailed
explanation of a function, class, or module. 

Commenting Out Code Using Triple-Quoted Strings

During development and experimentation, you might need to temporarily disable a code section without deleting it. Commenting out code is a convenient way to achieve this. While single-line or multi-line comments work, comments inserted using triple-quoted strings are recommended. By enclosing the code you want to comment out in triple quotes (“”” or ”’), you can effectively comment out large sections of code. This prevents execution and makes it easier to return to the previous working state later.

For example:

def some_function():
    print("This function does something!")

The code block inside the triple quotes is commented out, meaning it won’t execute. This is particularly useful for temporary comments, when you anticipate needing them later.


Comments are a vital part of Python programming, promoting code organization and making it easier for others to understand and maintain. By following best practices, such as coding with one statement per line, your code becomes more maintainable and readable.

5) Whitespace

In Python, whitespace refers to spaces, tabs, or blank lines used to separate code parts. While optional, their use is strongly recommended because they enhance code readability, organization, and overall quality.

Use of Whitespace for Readability

Readability is crucial in Python code. Readable code is easy to understand, reduces errors, and simplifies codebase maintenance. Effective whitespace usage enhances readability by separating code blocks, grouping related code, and providing visual clarity. For example:

if score >= 90:
  grade = "A"
elif score >= 80:
  grade = "B"
  grade = "C"

This code is much easier to read than the same code without whitespace. Whitespace organizes the code logically, making it easier to follow the program’s logic.

Importance of Whitespace between Keywords and Identifiers

Whitespace is essential between keywords and identifiers in Python. Keywords are reserved words with special meanings, and identifiers are user-defined names representing variables, functions, classes, and other objects. Separating them with whitespace ensures the Python interpreter identifies them correctly. For example:

if score >= 90:
  grade= "A"

In this code, the keyword “if” and the identifier “score,” as well as the assignment operator “=” and the string “A,” are not separated by whitespace. This makes the code harder to read and can be confusing, potentially leading to errors.

Academic Nature of Whitespace Usage

Whitespace is an academic topic in programming languages, and different conventions exist for its usage in different languages. While various languages have their conventions, Python takes its whitespace usage more seriously than most. Python’s strong emphasis on whitespace distinguishes it from other languages, resulting in clean, readable, and visually appealing code.

6) Deep Dive: Fortran and Whitespace

Fortran is a programming language with a history spanning over 60 years, significantly contributing to scientific computing and data analysis. Unlike Python, Fortran ignores whitespace in the source code. This practice makes older Fortran code often unsuitable for reuse, updating, and modification.

Ignoring whitespace makes code difficult to read and increases the risk of programming errors, especially in complex code. This has become a significant issue in scientific programming. While widely accepted in the past, programs that ignore whitespace are challenging to read or modify by newer generations of programmers.

Difficulty in Reading and Potential for Errors

When whitespace is ignored, distinguishing different program parts becomes difficult, often leading to errors. This has been a significant problem, particularly in scientific programming. Though accepted in the past, programs ignoring whitespace are difficult to read or modify by newer generations of programmers.

NASA’s Example of Programming Error Due to Whitespace

NASA experienced the dangers of ignoring whitespace when, on January 4, 1999, it lost the Mars Climate Orbiter spacecraft due to a programming error. The investigation revealed the error occurred in the spacecraft’s navigation system, where the NASA team used metric units, while the program read them as British Imperial units. Ignoring whitespace was a contributing factor to this catastrophic event.


Whitespace use in Python is highly recommended because it improves code readability, makes it easier to understand, and reduces errors. These practices are academically accepted and crucial to the overall sustainability of the code.

As seen with Fortran and the Mars Climate Orbiter incident, the importance of whitespace usage in programming languages can have significant impacts. When writing Python code, apply best practices of using whitespace effectively to make the program more maintainable for years to come.

This article has explored essential topics related to Python programming, including statements, line continuation, comments, and whitespace. Python’s emphasis on readability makes whitespace vital in enhancing code organization and readability. Correct whitespace usage makes your code stand out and avoids potential errors, ensuring sustainability for years to come.

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