Variable Assignment in Python

Python lets you create variables simply by assigning a value to the variable, without the need to declare the variable upfront. The value assigned to a variable determines the variable type. Different types may support some operations that others don't. 

Rules for variable names

• names can not start with a number
• names can not contain spaces, use _ intead

names can not contain any of these symbols:

:'",<>/?|\!@#%^&*~-+

it's considered best practice (PEP8) that names are lowercase with underscores

• avoid using Python built-in keywords like list and str
• avoid using the single characters l (lowercase letter el), O (uppercase letter oh) and I (uppercase letter eye) as they can be confused with 1 and 0

Dynamic Typing

Python uses dynamic typing, meaning you can reassign variables to different data types. This makes Python very flexible in assigning data types; it differs from other languages that are statically typed.

my_dogs = 2
my_dogs

my_dogs = ['Sammy', 'Frankie']
my_dogs

Pros and Cons of Dynamic Typing

Pros of Dynamic Typing

• very easy to work with
• faster development time

Cons of Dynamic Typing

• may result in unexpected bugs!
• you need to be aware of type()

Assigning Variables

The variable assignment follows name = object, where a single equals sign = is an assignment operator

a = 5
a

Here we assigned the integer object 5 to the variable name a. Let's assign a to something else:

a = 10
a

You can now use a in place of the number 10:

a + a

Reassigning Variables

Python lets you reassign variables with a reference to the same object.

a = a + 10
print(a)

There's actually a shortcut for this. Python lets you add, subtract, multiply and divide numbers with reassignment using +=, -=, *=, and /=.

a += 10
print(a)
#############
a *= 2
print(a)

Determining variable type with type()

You can check what type of object is assigned to a variable using Python's built-in type() function. Common data types include:

• int (for integer)
• float
• str (for string)
• list
• tuple
• dict (for dictionary)
• set
• bool (for Boolean True/False) 

a=5
type(a)

a = (1,2)
type(a)

Simple Exercise

This shows how variables make calculations more readable and easier to follow.

my_income = 100
tax_rate = 0.1
my_taxes = my_income * tax_rate
print(my_taxes)

You should now understand the basics of variable assignment and reassignment in Python.