Python Syntax

Execute Python Syntax

As we learned in the previous page, Python syntax can be executed by writing directly in the Command Line:

>>> print("Hello, World!")
Hello, World!

Or by creating a Python file on the server, using the .py file extension, and running it in the Command Line:

C:\Users\Your Name>python myfile.py

Python Indentation

Indentation refers to the spaces at the beginning of a code line.

Where in other programming languages the indentation in code is for readability only, the indentation in Python is very important.

Python uses indentation to indicate a block of code.

Example:
if 5 > 2:
    print("Five is greater than two!")

Python will give you an error if you skip the indentation:

Example (Syntax Error):
if 5 > 2:
print("Five is greater than two!")

The number of spaces is up to you as a programmer, the most common use is four, but it has to be at least one.

Example:
if 5 > 2:
 print("Five is greater than two!") 

if 5 > 2:
        print("Five is greater than two!")

You have to use the same number of spaces in the same block of code, otherwise Python will give you an error:

Example (Syntax Error):
if 5 > 2:
 print("Five is greater than two!")
        print("Five is greater than two!")

Python Variables

In Python, a variable is created when you assign a value to it:

Example:
x = 5
y = "Hello, World!"

Python has no command for declaring a variable.

You will learn more about variables in the Python Variables chapter.

Comments

Python has commenting capability for the purpose of in-code documentation.

Comments start with a #, and Python will render the rest of the line as a comment:

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

Statements

A computer program is a list of "instructions" to be "executed" by a computer. In a programming language, these programming instructions are called statements.

The following statement prints the text "Python is fun!" to the screen:

Example:
print("Python is fun!")

In Python, a statement usually ends when the line ends. You do not need to use a semicolon (;) like in many other programming languages (for example, Java or C).

Many Statements

Most Python programs contain many statements. The statements are executed one by one, in the same order as they are written:

Example:
print("Hello World!")
print("Have a good day.")
print("Learning Python is fun!")

From the example above, we have three statements:

  1. The first statement is executed first (print("Hello World!")).
  2. Then the second statement is executed (print("Have a good day.")).
  3. And at last, the third statement is executed (print("Learning Python is fun!")).

Semicolons (Optional, Rarely Used)

Semicolons are optional in Python. You can write multiple statements on one line by separating them with ; but this is rarely used because it makes it hard to read:

Example:
print("Hello"); print("How are you?"); print("Bye bye!")

However, if you put two statements on the same line without a separator (newline or ;), Python will give an error:

Example (Syntax Error):
print("Python is fun!") print("Really!")

Best practice: Put each statement on its own line so your code is easy to understand.

Challenge: Statements

Test your understanding of Python statements by completing a small coding challenge.

Instructions: Complete the following steps inside the editor:

Challenge Template:
# Print "Hello World!"
print("Hello World!")

# Print "Have a good day."
print("Have a good day.")

# Print "Learning Python is fun!"
print("Learning Python is fun!")