Python - Comments

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Python Comments

Python comments are programmer-readable explanation or annotations in the Python source code. They are added with the purpose of making the source code easier for humans to understand, and are ignored by Python interpreter. Comments enhance the readability of the code and help the programmers to understand the code very carefully.

Example

If we execute the code given below, the output produced will simply print "Hello, World!" to the console, as comments are ignored by the Python interpreter and do not affect the execution of the program −

# This is a comment
print("Hello, World!")

Python supports three types of comments as shown below −

  • Single-line comments
  • Multi-line comments
  • Docstring Comments

Single Line Comments in Python

Single-line comments in Python start with a hash symbol (#) and extend to the end of the line. They are used to provide short explanations or notes about the code. They can be placed on their own line above the code they describe, or at the end of a line of code (known as an inline comment) to provide context or clarification about that specific line.

Example: Standalone Single-Line Comment

A standalone single-line comment is a comment that occupies an entire line by itself, starting with a hash symbol (#). It is placed above the code it describes or annotates.

In this example, the standalone single-line comment is placed above the "greet" function "−

# Standalone single line comment is placed here
def greet():
   print("Hello, World!")
greet()

Example: Inline Single-Line Comment

An inline single-line comment is a comment that appears on the same line as a piece of code, following the code and preceded by a hash symbol (#).

In here, the inline single-line comment follows the print("Hello, World!") statement −

print("Hello, World!")  # Inline single line comment is placed here

Multi Line Comments in Python

In Python, multi-line comments are used to provide longer explanations or notes that span multiple lines. While Python does not have a specific syntax for multi-line comments, there are two common ways to achieve this: consecutive single-line comments and triple-quoted strings −

Consecutive Single-Line Comments

Consecutive single-line comments refers to using the hash symbol (#) at the beginning of each line. This method is often used for longer explanations or to section off parts of the code.

Example

In this example, multiple lines of comments are used to explain the purpose and logic of the factorial function −

# This function calculates the factorial of a number
# using an iterative approach. The factorial of a number
# n is the product of all positive integers less than or
# equal to n. For example, factorial(5) is 5*4*3*2*1 = 120.
def factorial(n):
   if n < 0:
      return "Factorial is not defined for negative numbers"
   result = 1
   for i in range(1, n + 1):
      result *= i
   return result

number = 5
print(f"The factorial of {number} is {factorial(number)}")

Multi Line Comment Using Triple Quoted Strings

We can use triple-quoted strings (''' or """) to create multi-line comments. These strings are technically string literals but can be used as comments if they are not assigned to any variable or used in expressions.

This pattern is often used for block comments or when documenting sections of code that require detailed explanations.

Example

Here, the triple-quoted string provides a detailed explanation of the "gcd" function, describing its purpose and the algorithm used −

"""
This function calculates the greatest common divisor (GCD)
of two numbers using the Euclidean algorithm. The GCD of
two numbers is the largest number that divides both of them
without leaving a remainder.
"""
def gcd(a, b):
   while b:
      a, b = b, a % b
   return a

result = gcd(48, 18)
print("The GCD of 48 and 18 is:", result)

Using Comments for Documentation

In Python, documentation comments, also known as docstrings, provide a way to incorporate documentation within your code. This can be useful for explaining the purpose and usage of modules, classes, functions, and methods. Effective use of documentation comments helps other developers understand your code and its purpose without needing to read through all the details of the implementation.

Python Docstrings

In Python, docstrings are a special type of comment that is used to document modules, classes, functions, and methods. They are written using triple quotes (''' or """) and are placed immediately after the definition of the entity they document.

Docstrings can be accessed programmatically, making them an integral part of Python’s built-in documentation tools.

Example of a Function Docstring

def greet(name):
   """
   This function greets the person whose name is passed as a parameter.

   Parameters:
   name (str): The name of the person to greet

   Returns:
   None
   """
   print(f"Hello, {name}!")
greet("Alice")

Accessing Docstrings

Docstrings can be accessed using the .__doc__ attribute or the help() function. This makes it easy to view the documentation for any module, class, function, or method directly from the interactive Python shell or within the code.

Example: Using the .__doc__ attribute

def greet(name):
    """
    This function greets the person whose name is passed as a parameter.

    Parameters:
    name (str): The name of the person to greet

    Returns:
    None
    """
print(greet.__doc__)

Example: Using the help() Function

def greet(name):
    """
    This function greets the person whose name is passed as a parameter.

    Parameters:
    name (str): The name of the person to greet

    Returns:
    None
    """
help(greet)
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