How to write Comments in Python3?

Comments are text notes added to the program to provide explanatory information about the source code. They are used in a programming language to document the program and remind programmers of what tricky things they just did with the code and also help the later generation for understanding and maintenance of code. The compiler considers these as non-executable statements. Since comments do not execute, when you run a program you will not see any indication of the comment in the output.

Syntax: The hash(#) symbol denotes the starting of a comment in Python.  

# This is a comment in Python

Example:

python3

# This is the syntax of a comment in Python
print("GFG")

# Comments dont have any effect on the interpreter / output

Output :

GFG

Comments should be made at the same indent as the code it is commenting on.

python3

def GFG():

  # Since, this comment is inside a function
  # It would have indent same as the function body
  print("GeeksforGeeks")

  for i in range(1, 2):

    # Be careful of indentation
    # This comment is inside the body of for loop
    print("Welcome to Comments in Python")

# This comment is again outside the body
# of function so it wont have any indent.

print("Hello !!")
GFG()

Output

Hello!!
GeeksforGeeks
Welcome to Comments in Python

Types of Comments

1. Single-Line Comments: Comments starting with a ‘#’ and whitespace are called single-line comments in Python. These comments can only stretch to a single line and are the only way for comments in Python. e.g.

# This a single line comment.

2. Multi-line (Block) comments: Unlike other programming languages Python doesn’t support multi-line comment blocks out of the box. However we can use consecutive # single-line comments to comment out multiple lines of code. Some examples of block comments-

# This type of comments can serve
# both as a single-line as well
# as multi-line (block) in Python.

3. Inline Style comments: Inline comments occur on the same line of a statement, following the code itself. Generally, inline comments look like this:

x = 3        # This is called an inline comment
a = b + c    # Adding value of 'b' and 'c' to 'a'

4. Docstring comments: Python documentation strings (or docstrings) provide a convenient way of associating documentation with Python modules, functions, classes, and methods. It’s specified in source code that is used, like a comment, to document a specific segment of code. Unlike conventional source code comments, the docstring should describe what the function does, not how.

Example: 

python3

def my_function():
    """Demonstrates docstrings and does nothing really."""

    return None


print("Using __doc__:")
print(my_function.__doc__)

print("Using help:")
help(my_function)

Output:

Using __doc__:
Demonstrates docstrings and does nothing really.
Using help:
Help on function my_function in module __main__:
my_function()
    Demonstrates docstrings and does nothing really.

Advantages and Uses of Comments:

Planning and reviewing: In the comments, we can write the pseudocode which we planned before writing the source code. Pseudocode is a mixture of natural language and high-level programming language. This helps in reviewing the source code more easily because pseudocode is more understandable than the program. 

Example:

python3

# This function is adding two given numbers
def addition(a, b):

  # storing the sum of given numbers in 'c'.
  c = a + b

  # returning the sum here
  return c

# passing the value of a and b to addition()
a = 10
b = 3
sum = addition(a, b)

# printing the sum calculated by above function
print(sum)

Output :

13

Debugging: The brute force method is a common method of debugging. In this approach, print statements are inserted throughout the program to print the intermediate values with the hope that some of the printed values will help to identify the errors. After doing debugging we comment on those print statements. Hence comment is also used for debugging.

python3

a = 12

if(a == 12):
  print("True")

# elif(a == 0):
  # print("False")

else:
  print("Debugging")

Output :

True

Learn Python 3 at your own pace with our well-structured tutorial: Python 3 Tutorial