Python Comments and Variables
Comments can be used to explain Python code.
Comments can be used to make the code more readable.
Comments can be used to prevent execution when testing code.
Creating a Comment:
Comments start with a #, and Python will ignore them
Comments can be placed at the end of a line, and Python will ignore the rest of the line:
A comment does not have to be text that explains the code, it can also be used to prevent Python from executing code:
Multi Line Comments:
Python does not really have a syntax for multi line comments.
To add a multiline comment you could insert a # for each line:
Python Variables
Variables:
Variables are containers for storing data values.
Creating Variables:
Python has no command for declaring a variable.
A variable is created the moment you first assign a value to it.
Variables do not need to be declared with any particular type, and can even change type after they have been set.
Casting:
If you want to specify the data type of a variable, this can be done with casting.
Get the Type:
You can get the data type of a variable with the type() function.
Single or Double Quotes?
String variables can be declared either by using single or double quotes:
Case-Sensitive:
Variable names are case-sensitive.
Python - Variable Names:
Variable Names
A variable can have a short name (like x and y) or a more descriptive name (age, carname, total_volume). Rules for Python variables:
- A variable name must start with a letter or the underscore character
- A variable name cannot start with a number
- A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ )
- Variable names are case-sensitive (age, Age and AGE are three different variables)
Multi Words Variable Names:
Variable names with more than one word can be difficult to read.
There are several techniques you can use to make them more readable:
Camel Case:
Each word, except the first, starts with a capital letter:
Pascal Case:
Each word starts with a capital letter:
Snake Case:
Each word is separated by an underscore character:
Assign Multiple Values:
Many Values to Multiple Variables:
Python allows you to assign values to multiple variables in one line:
One Value to Multiple Variables:
And you can assign the same value to multiple variables in one line:
Unpack a Collection:
If you have a collection of values in a list, tuple etc. Python allows you to extract the values into variables. This is called unpacking.
Python - Output Variables:
Output Variables
The Python print() function is often used to output variables.
In the print() function, you output multiple variables, separated by a comma:
You can also use the + operator to output multiple variables:
For numbers, the + character works as a mathematical operator:
In the print() function, when you try to combine a string and a number with the + operator, Python will give you an error:
The best way to output multiple variables in the print() function is to separate them with commas, which even support different data types:
Python - Global Variables:
Global Variables:
Variables that are created outside of a function (as in all of the examples above) are known as global variables.
Global variables can be used by everyone, both inside of functions and outside.
The global Keyword:
Normally, when you create a variable inside a function, that variable is local, and can only be used inside that function.
To create a global variable inside a function, you can use the global keyword.
