1-Variables

Notebook

Link to the Google Colaboratory notebook: 1-Variables

Variables

Variables store data values and can be used throughout the program.

Python variables

In Python, you don’t need to declare the variable and the type.

A Python variable is created and a place in memory is allocated when you assign a value to it.

To create a variable, use the = sign: on the left is the name of the variable, and on the right is the value.

counter = 100 # An integer variable
name = "Evry" # A string variable
amount = 17.2 # A float variable

You can print a variable using the print function:

counter = 100 # An integer variable
name = "Evry" # A string variable
print(counter)
print(name)

100
Evry

String quotes

String variables can be declared using either single or double quotes:

name = "Evry" 
# is the same as 
name = 'Evry'

It is nonetheless recommended to keep the same notation for the strings. If you use single quotes, be consistent with it.

Variable names

Variables can have short (like x, y, ..,) or long (age, family_name, …) names.

There are 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)
• A variable name cannot be any of the Python keywords.

Reserved keywords

Here is a list of Python keywords that are reserved. Your variables, name of function, class should not be named with those words.

Python reserved words

and	as	assert	break
class	continue	def	del
elif	else	except	False
finally	for	from	global
in	is	lambda	None
nonlocal	not	or	pass
raise	return	True	try
while	with	yield

Valid names

myname="Evry" 
my_name="Evry" 
myname2="Evry" 
_my_name="Evry" 
myName="Evry" 
MYNAME="Evry" 

Non-valid names

"""
10myname="Evry" 
my-name="Evry" 
my name="Evry" 
"""

Assignment of multiple values

Python allows to assign values to multiple variables in one line:

city, age, country = "Evry", 77, "France"
print(city)
print(age)
print(country)

Evry
77
France

Output variables

The print function allows you to output variables.

You can output multiple variables by separated them with a ,:

city, age, country = "Evry", 77, "France"
print(city, age, country)

Evry 77 France

You can also use + to output multiple variables:

city, country = "Evry ", "France"
print(city + country)

Evry France

Note

Note that when you want to print multiple strings, the + doesn’t add a space.

You need to add it manually.

city, country = "Evry", "France"
print(city + country)

EvryFrance

The + is working for strings, but act differently for other types:

x,y = 5, 10
print(x+y)

15

Important

Note that you can’t add a string and an integer with the + sign.

To print both of them, you can either separate them with ,, or cast the integer using the str function:

name, age = "Evry", 77
# print(name + age) # It will raise an error
print(name, age)
print(name + str(age))

Evry 77
Evry77