Variable Assignment

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.

In [1]:
my_dogs = 2
In [2]:
my_dogs
Out[2]:
2
In [3]:
my_dogs = ['Sammy', 'Frankie']
In [4]:
my_dogs
Out[4]:
['Sammy', 'Frankie']

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

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

In [5]:
a = 5
In [7]:
a
Out[7]:
5

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

In [8]:
a = 10
In [9]:
a
Out[9]:
10

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

In [10]:
a + a
Out[10]:
20

Reassigning Variables

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

In [11]:
a = a + 10
In [12]:
a
Out[12]:
20

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

In [13]:
a += 10
In [14]:
a
Out[14]:
30
In [16]:
a *= 2
In [17]:
a
Out[17]:
120

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)
In [18]:
type(a)
Out[18]:
int
In [19]:
a = (1,2)
In [20]:
type(a)
Out[20]:
tuple

Simple Exercise

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

In [21]:
my_income = 100
tax_rate = 0.1
my_taxes = my_income * tax_rate
In [20]:
my_taxes
Out[20]:
10.0

Great! You should now understand the basics of variable assignment and reassignment in Python.
Up next, we'll learn about strings!