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5.2. Numeric Data Types

Python has many useful built-in data types. Python variables can store different types of data based on a variable’s data type. A variable’s data type is created dynamically, without the need to explicitly define a data type when the variable is created.

It is useful for problem solvers to understand a couple of Python’s core data types in order to write well-constructed code.

5.2.1. A review of variable assignment in Python

Recall from the previous chapter that variables in Python are defined with the assignment operator, the equals sign =. To define a variable in Python, the variable name is written first, then the assignment operator = followed by a value or expression.

The general syntax to assign a value to variable name is below:

variable_name = value

Variable names in Python must adhere to the following rules:

  • variable names must start with a letter

  • variable names can only contain letters, numbers and the underscore character _

  • variable names can not contain spaces or punctuation

  • variable names are not enclosed in quotes or brackets

Below is a discussion of a few different built-in data types in Python.

5.2.2. Integers

Integers are one of the Python data types. An integer is a whole number, negative, positive or zero. In Python, integer variables are defined by assigning a whole number to a variable. Python’s type() function can be used to determine the data type of a variable.

>>> a = 5
>>> type(a)
<class 'int'>

The output <class 'int'> indicates the variable a is an integer. Integers can be negative or zero.

>>> b = -2
>>> type(b)
<class 'int'>
>>> z = 0
>>> type(z)
<class 'int'>

5.2.3. Floating Point Numbers

Floating point numbers or floats are another Python data type. Floats are decimals, positive, negative and zero. Floats can also be represented by numbers in scientific notation which contain exponents.

Both a lower case e or an upper case E can be used to define floats in scientific notation. In Python, a float can be defined using a decimal point . when a variable is assigned.

>>> c = 6.2
>>> type(c)
<class 'float'>
>>> d = -0.03
>>> type(d)
<class 'float'>
>>> Na = 6.02e23
>>> Na
6.02e+23
>>> type(Na)
<class 'float'>

To define a variable as a float instead of an integer, even if the variable is assigned a whole number, a trailing decimal point . is used. Note the difference when a decimal point . comes after a whole number:

>>> g = 5
>>> type(g)
<class 'int'>
>>> f = 5.
>>> type(r)
<class 'float'>

5.2.4. Complex Numbers

Another useful numeric data type for problem solvers is the complex number data type. A complex number is defined in Python using a real component + an imaginary component j. The letter j must be used to denote the imaginary component. Using the letter i to define a complex number returns an error in Python.

>>> comp = 4 + 2j
>>> type(comp)
<class 'complex'>

>>> comp2 = 4 + 2i
              ^
SyntaxError: invalid syntax

Imaginary numbers can be added to integers and floats.

>>> intgr = 3
>>> type(intgr)
<class 'int'>

>>> comp_sum = comp + intgr
>>> print(comp_sum)
(7+2j)

>>> flt = 2.1
>>> comp_sum = comp + flt
>>> print(comp_sum)
(6.1+2j)