What is float in python?

What is a float in Python?

Short answer: a float is Python's type for numbers with a decimal point, like 19.99, 3.5 or -0.25. You get one when you write a number with a dot, when you divide with /, or when you convert text with float("3.5").

price = 19.99
print(type(price))      # <class 'float'>
print(7 / 2)            # 3.5
print(float("3.5") + 1) # 4.5

Floats are stored in binary, so some decimals are approximate: 0.1 + 0.2 gives 0.30000000000000004. Round them to show them, and use Decimal for money.

A float is a number with decimals, float() converts text into one and round() hides the tiny binary errors when you show it.

Floats at a glance

How to create a float

Any number with a decimal point is a float, even if the decimals are zero:

a = 3.0
b = -0.25
c = 1e3        # 1000.0, scientific notation
 
print(type(a), type(c))   # <class 'float'> <class 'float'>

Mixing an int and a float gives a float: 5 + 2.0 is 7.0. The / operator always returns a float, even when the division is exact: 10 / 2 is 5.0.

Convert to float with float()

float() turns text and integers into floats. It's what you need after input(), which always returns text:

height_text = input("Height in meters: ")   # "1.75"
height = float(height_text)
print(height * 100)                      # 175.0
 
print(float("  2.5 "))   # 2.5  spaces are ignored
print(float(7))          # 7.0
print(float(True))       # 1.0

The text must use a dot as the decimal separator. A comma fails:

float("3,5")
# ValueError: could not convert string to float: '3,5'
 
float("3,5".replace(",", "."))   # 3.5

To convert a float to an integer, int() drops the decimals without rounding: int(3.99) is 3. To go from the text "3.5" to an integer, convert it to float first: int(float("3.5")).

Why 0.1 + 0.2 is not 0.3

Computers store floats in binary, and many decimals, like 0.1, have no exact binary form. Python keeps the closest value it can, so tiny errors appear:

print(0.1 + 0.2)          # 0.30000000000000004
print(0.1 + 0.2 == 0.3)   # False

This happens in every language that uses standard floats, not only Python. There are three ways to handle it:

import math
from decimal import Decimal
 
print(round(0.1 + 0.2, 2))                 # 0.3   to show it
print(math.isclose(0.1 + 0.2, 0.3))        # True  to compare
print(Decimal("0.1") + Decimal("0.2"))     # 0.3   exact, for money

Never compare floats with ==. Use math.isclose(), and create Decimal values from text, not from floats.

Format floats for display

Keep the full value for calculations and format it only when you show it:

total = 1234567.891
 
print(f"{total:.2f}")    # 1234567.89
print(f"{total:,.2f}")   # 1,234,567.89
print(f"{0.256:.1%}")    # 25.6%

How big and how precise a float is

Python floats are 64-bit numbers. They keep about 15 to 17 significant digits, and the largest value is about 1.8e308:

import sys
print(sys.float_info.max)   # 1.7976931348623157e+308
print(sys.float_info.dig)   # 15
print(1e308 * 10)           # inf

Integers in Python have no size limit, but floats do. For very precise calculations, use Decimal or fractions.Fraction.

Check if a value is a float

x = 3.0
 
print(isinstance(x, float))   # True
print(x.is_integer())         # True, it has no decimal part
print((3.5).is_integer())     # False

Use AI to work with floats

An assistant like ChatGPT, Claude or GitHub Copilot can explain a strange decimal result and suggest the right type. These three prompts are ready to copy.

1. Explain a result

In Python, [your calculation] returns [the result] and I expected [what you expected].
Explain why and show me how to get the right result.

2. Choose a type

I'm working with [prices / measurements / percentages] in Python.
Should I use float, int or Decimal? Show me an example with my data: [paste a sample].

3. Fix a conversion

This Python line: [paste it] gives this error: [paste the error].
The value comes from [input() / a CSV / an API]. Show me how to convert it safely.

Check the answer with a few values you can calculate by hand.

Common problems with floats in Python

Related guides

• How to round in Python
• How to multiply in Python
• Python double slash (//) operator
• What does == mean in Python
• How to get the length of a list in Python
• How to check your Python version