Variable Assignment in Python

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Written by Aayush Saini · 2 minute read · Jun 14, 2020 . Python, 41

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. 


 

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