Python Variables
Creating Variables
variables help us reference a piece of data for later use.
name = "Ahmed"
height_cm = 180
weight_kg = 85.5
A variable gives us an easy-to-use shortcut to a piece of data. Whenever we use the variable name in our code, it will be replaced with the original piece of data.
In this case, one of our variables name
and its vale is Ahmed
. Another variable is height_cm
and its value is 180
. We define variables using an equal sign =
.
Variables Names Rules
When defining variables, we need to follow a few rules:
- Must start with a letter (usually lowercase)
- After first litter, we can use letters/numbers/underscores
- No space or special characters
- Variable names a re case sensitive (my_var is different from MY_VAR)
# Valid Variables
baby_weight
bw
baby1
b_1
# Invalid Variables
baby-weight
bw!
baby@1
Error Messages
Let's see what happens when we try to use an invalid variable name. The variable baby-weight
is invalid because of the hyphen -
.
File "main.py", line 1
baby-weight = 3
^
SyntaxError: cannot assign to operator
Floats and Stings
Variables come in many flavors. Two important flavors are floats and strings.
- Floats represent either integers or decimals
height = 180
weight = 85.5
- Strings represent text; can contain letters, numbers, spaces, and special characters
name = 'Ahmed'
Job = "Data Analytics & Visualization Engineer"
We define a string by putting either single ''
or double ""
quotes around a piece of text.
Common String Mistakes
It's easy to get errors when working with strings. If you get one, there are two likely causes.
- Without quotes
last_name = Gouda
, you'll get a NameError.
File "main.py", line 1, in <module>
last_name = Gouda
NameError: name 'Gouda' is not defined
If you forgot to put quotation marks around your string, Python will thing that your string is a variable. And if that variable wasn't previously defined, you'll get a NameError.
- Different quotation marks
last_name = "Gouda'
, you'll get a SyntaxError.
File "main.py", line 9
last_name = "Gouda'
^
SyntaxError: EOL while scanning string literal
If you mix single '
and double "
quotes, you'll get a syntax error.
Displaying Variables
name = "Ahmed"
height_cm = 180
weight_kg = 85.5
print(height_cm)
Output:
180
If we want to know the current value of one of our variables, we can use print
. We simply type the word print
and put our variable name inside of the parentheses print(name)
.