Basic Data Types & Variables

Thomas J. Kennedy

Contents:

1 Overview

1 Overview

Python has most of the basic datatypes that you will find in C++, Java, and Rust… with one exception.

The datatypes covered in this discussion focus on those that are commonly used (e.g., int in C++ or Java). It is not an exhaustive list.

Description	Python	C++	Java	Rust
boolean value	`bool`	`bool`	`boolean`	`bool`
32-bit integer	`int`	`int`	`int`	`i32`
64-bit floating point	`float`	`double`	`double`	`f64`
character		`char`	`char`	`char`
null-terminated (C-style) string		`char*`		`&str`
string	`str`	`std::string`	`String`	`String`

The Python float is technically more complicated than just a 64-bit floating point value. However, a simplified perspective will work for now.

You probably noticed that Python does not have a character type (char). In most code… a Python string (str) is used instead (albeit with only a single letter at index zero).

The Python string (str) is analogous to a C++ std::string and Java String (and Rust String). It is a full-fledged class with functions such as len, startswith, and replace.

2 Example Values

Let us take the first two columns from the comparison table…

Description	Python
boolean value	`bool`
32-bit integer	`int`
64-bit floating point	`float`
character
null-terminated (C-style) string
string	`str`

I think the description column (along with the rows where Python has no equivalent type) can be removed and replaced with example values.

Python	Example Values
`bool`	`True` or `False`
`int`	`7`, `0`, or `-40`
`float`	`3.14`
`str`	`"Sample String"`

Note that boolean values in Python are capitalized (i.e., True or False) unlike C++, Java, and Rust (i.e., true and false). This is one of the common mistakes when learning Python)

2.1 bool

The bool type is normally found within a conditional block. However, the ternary operator does exist in Python…

is_blue = True if selected_color.title() == "Blue" else False

But… the expression itself is already a boolean expressiion.

is_blue = selected_color.title() == "Blue"

2.2 int

The integer type behaves in Python as it does in C++ and Java… complete with integer division.

Operation	Expression	Result
Addition	`5 + 2`	`7`
Subtraction	`7 - 12`	`-5`
Multiplication	`8 * 3`	`24`
Division	`7 / 2`	`3.5`
Division	`7 // 2`	`3`
Modulus	`7 % 2`	`1`
Exponentiation	`8 ** 2`	`64`

Take note of the two divisions. Python 3 (specifically PEP 238) introduced a dedicated // operator for integer division.

Unlike most languages where a pow or fpow function is needed for exponentiation… Python included the ** operator.

2.3 float

Python’s float type suffers from the same floating point precision issue as analogous types in other languages. (If you are truly curious… CS 417, Computational Methods, discusses why all floating point numbers suffer from precision issues.)

float provides the same operators as int… with the exception of //.

2.4 str

The str type will be covered in a lecture during the next module. *If you are curious… feel free to look ahead.