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Python Basics : Variables

by shedboy71

A variable is an identifier that holds a value.

An Identifier is used to identify the literals used in the program. There a few rules that are used in the naming of an identifier, lets take a look at these.

  • The first character of the variable must start with a letter or the underscore character
  • All characters except the first character can be lower case(a-z), upper case (A-Z), an underscore, or a numerical digit (0-9).
  • An identifier must not contain any white space or special characters such as $, %, !,@, *(!, @, #, %, ^, &, *).
  • An identifier is case sensitive; for example, myname, MyName, Myname and MyName are not the same.

That last one is a biggie, lets look at examples of legal and illegal names

 

#Legal variable names:
myname = "python"
my_name = "python"
_my_name = "python"
myName = "python"
MYNAME = "python"
myname1 = "python"

#Illegal variable names:
1myname = "python"
my-name = "python"
my name = "python

 

Python does not require us to declare a variable before using it. It allows us to create a variable at the required time. You also do not need to declare explicitly a variable in Python. When we assign a value to the variable, that variable is declared automatically.
The equal (=) operator is used to assign value to a variable.

Let’s look at a basic example

x = 8
y = "python"
print(x)
print(y)

You should see something like this in the REPL window

MicroPython v1.9.2-34-gd64154c73 on 2017-09-01; micro:bit v1.0.1 with nRF51822
Type "help()" for more information.
>>> 8
python

Variables can even change type after they have been set. Lets see an example of that where we have a variable called x and it will be an int first and then we will change it to a string

 

x = 8
print(x)
x = "python"
print(x)

Now run this example

MicroPython v1.9.2-34-gd64154c73 on 2017-09-01; micro:bit v1.0.1 with nRF51822
Type "help()" for more information.
>>> 8
python

String variables

A String variable can be declared either by using single or double quotes, like this

mylanguage1 = "Python"
print(mylanguage1)
mylanguage2 = 'Python'
print(mylanguage2)

When you run this you will see the following

MicroPython v1.9.2-34-gd64154c73 on 2017-09-01; micro:bit v1.0.1 with nRF51822
Type "help()" for more information.
>>> Python
Python

 

Multiple Values and variables

Python allows you to assign values to multiple variables in one line
Python also allows you to assign the same value to multiple variables in one line

x, y, z = "esp8266", "esp32", "microbit"
print(x)
print(y)
print(z)

x = y = z = "microbit"
print(x)
print(y)
print(z)

Run this and you will see something like this

MicroPython v1.9.2-34-gd64154c73 on 2017-09-01; micro:bit v1.0.1 with nRF51822
Type "help()" for more information.
>>> 
>>> esp8266
esp32
microbit
microbit
microbit
microbit

 

Using the + character

You can use the + character to do the following

You can combine both text and a variable
You can add a variable to another variable
You can add numbers

 

x = "microcontroller"
print("ESP32 is a " + x)

x = "ESP32 is a "
y = "microcontroller"
z = x + y
print(z)

x = 7
y = 9
print(x + y)

You will see the following

MicroPython v1.9.2-34-gd64154c73 on 2017-09-01; micro:bit v1.0.1 with nRF51822
Type "help()" for more information.
>>> 
>>> ESP32 is a microcontroller
ESP32 is a microcontroller
16

Python will give you an error if you combine a string and a number

x = "ESP"
y = 32
print(x + y)

If you run this you will see an error like this

TypeError: can't convert 'int' object to str implicitly

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