Python String to Float Conversion - Be on the Right Side of Change

This article provides concise methods and code examples for various scenarios of string-to-float conversion.

Python String to Float

To convert a basic string to a float, use the float() function. This method is direct and works for strings that represent typical decimal numbers.

Here’s a minimal example:

number = "123.45"
converted = float(number)

This code converts the string "123.45" to the float 123.45.

Python String to Float with Comma

For strings with commas (common in European number formatting), replace commas with dots to conform to the standard float format before conversion.

Here’s a minimal example:

number = "123,45"
converted = float(number.replace(',', '.'))

This code changes the comma to a dot, making "123,45" compatible for conversion to 123.45.

Python String to Float with 2 Decimals

To convert a string to a float with exactly two decimal places, first convert the string to a float and then use round() to limit it to two decimals.

Here’s a minimal example:

number = "123.456"
converted = round(float(number), 2)

Here, "123.456" is first converted to a float, then rounded to 123.46.

Python String to Float Precision

For specific precision control during conversion, use format() with the float conversion. This method allows specifying the number of decimal places.

Here’s a minimal example:

number = "123.456"
converted = format(float(number), '.2f')

This method converts "123.456" to 123.46, formatted as a string with two decimal places.

Python String to Float Scientific Notation

Convert a string in scientific notation directly to a float using float(). This function handles scientific notation automatically.

Here’s a minimal example:

number = "1.2345e2"
converted = float(number)

This code converts the scientific notation "1.2345e2" to 123.45.

Python String to Float Array

To convert an array of string numbers into floats, use list comprehension, applying the float conversion to each element.

Here’s a minimal example:

numbers = ["1.2", "3.4", "5.6"]
converted = [float(num) for num in numbers]

Each string in the list ["1.2", "3.4", "5.6"] is converted to its float equivalent.

Python String to Float Ignore Letters

Remove non-numeric characters from a string using regular expressions (e.g., re.sub("[^0-9.]", "", number)) before converting it to a float.

Here’s a minimal example:

import re
number = "123abc"
converted = float(re.sub("[^0-9.]", "", number))

This code removes non-numeric characters from "123abc", resulting in 123.0.

Python String to Float Keep Precision

Convert a string to a float without any rounding to maintain the maximum precision present in the original string.

Here’s a minimal example:

number = "123.456789"
converted = float(number)

The string "123.456789" is converted to a float, preserving all its decimal places.

Python String to Float Thousand Separator

For strings with thousand separators, remove these separators before conversion. This is necessary for correct float interpretation.

Here’s a minimal example:

number = "1,234.56"
converted = float(number.replace(',', ''))

Here, the commas in "1,234.56" are removed, allowing the conversion to 1234.56.

Python String to Float Format

To convert a formatted string (like currency), first remove the formatting, then convert it to float.

Here’s a minimal example:

number = "$123.45"
converted = float(number.strip("$"))

This code strips the dollar sign from "$123.45" and converts it to 123.45.

Python String to Float NaN

Handle non-numeric strings by assigning NaN (Not a Number) if the conversion fails.

import math
number = "not a number"
try:
    converted = float(number)
except ValueError:
    converted = math.nan

If conversion fails, as with "not a number", it assigns math.nan.

Python String to Float Exception

Manage exceptions during conversion by using a try-except block. If conversion fails, handle it gracefully.

Here’s a minimal example:

number = "abc"
try:
    converted = float(number)
except ValueError:
    converted = "Conversion Error"

For strings that can’t be converted, like "abc", this method results in a custom error message "Conversion Error".

👉 Python Convert Float to String