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What is a floating point number in Python

Understanding Floating Point Numbers

When you first dip your toes into the world of programming, you encounter various types of data that you can manipulate. Among these, numbers are perhaps the most essential and universally understood. But not all numbers are created equal in the world of computing. In Python, as in many other programming languages, numbers are primarily divided into two types: integers and floating-point numbers. Let's focus on floating-point numbers and unravel what they are and how they work in Python.

The Basics of Floating Point Numbers

Imagine you're working with a ruler. On this ruler, you have markings for whole numbers (1, 2, 3, and so on), but what about the spaces between these markings? In the real world, we have fractions and decimals to describe these in-between values. In the digital world of Python, these are represented by floating-point numbers.

A floating-point number, or 'float' as it's commonly called, is a way to represent a number that has a decimal place. Floats are used when more precision is needed than what integers can provide. For example, if you were calculating currency or measurements that require exactness beyond whole units, floats would be your go-to data type.

# Example of a floating-point number
pi = 3.14159
print(pi)  # Output: 3.14159

How Python Handles Floating Point Numbers

Python follows the IEEE 754 standard for floating-point arithmetic, which is a technical specification for how computers represent and manipulate decimal numbers. This might sound complex, but it's just an agreed-upon way to ensure that when you work with decimals in Python, other programming languages understand them in the same way.

In Python, when you type a number with a decimal point, Python automatically treats it as a float.

# Python automatically identifies this as a float
earth_radius_km = 6371.0
print(type(earth_radius_km))  # Output: <class 'float'>

Precision in Floating Point Numbers

One of the quirks of floating-point numbers in any programming language is that they are not always as precise as you might expect. This is because of the way they are stored in a computer's memory. Computers use a binary system (comprising 0s and 1s) to represent all data, including numbers. Converting a decimal number to binary can sometimes result in a number that has a repeating binary fraction, which cannot be perfectly represented in a finite amount of space.

This is akin to trying to write down the exact value of 1/3 in decimal; you'd write 0.3333..., with the 3s going on forever. In a computer's binary memory, similar issues arise with certain decimal numbers.

Here's an example in Python where this precision issue becomes evident:

# A demonstration of floating point precision
sum = 0.1 + 0.2
print(sum)  # Output might not be the exact 0.3 you expect

Operations with Floating Point Numbers

Just like with whole numbers (integers), you can perform arithmetic operations with floating-point numbers in Python. You can add, subtract, multiply, and divide them.

# Arithmetic with floats
a = 5.5
b = 2.5

# Addition
print(a + b)  # Output: 8.0

# Subtraction
print(a - b)  # Output: 3.0

# Multiplication
print(a * b)  # Output: 13.75

# Division
print(a / b)  # Output: 2.2

Remember, when you perform arithmetic with an integer and a float, Python converts the result to a float to maintain precision.

Limitations and Edge Cases

While floating-point numbers are incredibly useful, they do have their limitations. One such limitation is their size. In Python, the maximum value a floating-point number can have is determined by the system's architecture. On most modern systems, a float has a 64-bit representation, which includes a sign bit, an exponent, and a significand (or mantissa). This allows for a very wide range of values, but it's not infinite.

Another edge case to be aware of is the concept of 'NaN' which stands for 'Not a Number'. This is a special floating-point value which is returned when the math does not result in a real number.

# Example of NaN in Python
not_a_number = float('nan')
print(not_a_number)  # Output: nan

Converting Between Integers and Floats

In Python, you can convert integers to floats and vice versa. This process is known as casting. When you cast an integer to a float, Python simply adds a decimal point and a zero to the number. However, when you cast a float to an integer, Python removes the decimal part without rounding.

# Casting an integer to a float
integer_value = 10
float_value = float(integer_value)
print(float_value)  # Output: 10.0

# Casting a float to an integer
float_value = 3.75
integer_value = int(float_value)
print(integer_value)  # Output: 3, not 4!

Practical Uses of Floats

Floating-point numbers are used in a multitude of applications. Anytime you need to work with a measurement that can have a fractional part, you'll likely use a float. This can range from scientific calculations, like determining the speed of light, to everyday uses, like calculating the tip at a restaurant.


Floating-point numbers are a fundamental part of programming, allowing you to work with a wide range of numeric values with precision. As you've seen, Python provides a straightforward approach to using floats, though it's important to be mindful of their limitations in terms of precision and range. Just like learning to balance on a floating log in water, mastering floating-point arithmetic takes practice and awareness of the potential for unexpected behavior. However, with the insights and examples provided, you're now better equipped to navigate the ebb and flow of floating-point numbers in your Python adventures. Keep experimenting, keep learning, and soon, handling floats will be as natural to you as counting on your fingers.