Convert String to Float in Python

The goal of converting a string to a float in Python is to ensure that numeric text, such as "33.28", can be used in mathematical operations. For example, if a variable contains the value "33.28", we may want to convert it to a float to perform operations like addition or division. Let's explore different methods to do this efficiently.

Using float()

float() function is an efficient way to convert a string into a floating-point number. As a built-in function, it returns a value of type float and works best with well-formatted numeric strings. However, if the input string is not a valid representation of a float, it raises a ValueError.

a = "33.28"
b = float(a)
print(type(b), b)

<class 'float'> 33.28

Using decimal.Decimal

Decimal class from Python’s decimal module provides precise decimal arithmetic, making it ideal for situations where accuracy is important , such as financial calculations. It converts a string into a Decimal object, effectively avoiding common floating-point rounding errors.

from decimal import Decimal

a = "33.28"
b = float(Decimal(a))
print(type(b), b)

<class 'float'> 33.28

Using eval()

eval() function reads and runs a string as a Python expression. It can turn a numeric string like "33.28" into a float. However, it's risky to use with untrusted input because it can run harmful code. It's best used only in safe and controlled situations.

a = "33.28"
b = eval(a)
print(type(b), b)

<class 'float'> 33.28

Using ast.literal_eval()

ast.literal_eval() function safely evaluates strings that contain Python literals, such as numbers or lists. It can securely convert a numeric string to a float. Unlike eval(), it doesn’t run any code, making it a safer option for handling user input.

import ast

a = "33.28"
b = ast.literal_eval(a)
print(type(b), b)

<class 'float'> 33.28

Related Articles:

• float() in Python
• eval in Python
• ast.literal_eval() in Python