Are you looking for a reliable way to check if a string is a number (float) using Python? If so, you’ve come to the right place. In this article, we’ll walk you through a step-by-step guide on how to check if a string is a number (float) in Python.

Before we get started, it’s important to understand that there are different ways to check if a string is a number (float) in Python. The most common approach is to use the isnumeric() and isdecimal() methods. However, these methods only work for strings that contain digits, and not for strings that contain a decimal point or a sign (+/-).

How do we check if a string is a number (float) in Python?

Regular expressions are a powerful tool that allows you to search and manipulate text based on patterns. In this case, we can use regular expressions to check if a string is a number (float) by matching it against a pattern that represents a number.

Here’s the Python code that checks if a string is a number (float) using regular expressions:

				
					import re

def is_float(str):
    pattern = re.compile("^[-+]?[0-9]*\.?[0-9]+([eE][-+]?[0-9]+)?$")
    return pattern.match(str) is not None

Let’s break down the regular expression pattern:

  • ^ matches the start of the string
  • [-+]? matches an optional sign (+/-)
  • [0-9]* matches zero or more digits
  • \.? matches an optional decimal point
  • [0-9]+ matches one or more digits
  • ([eE][-+]?[0-9]+)? matches an optional exponent (e/E), followed by an optional sign and one or more digits
  • $ matches the end of the string

So, the pattern matches strings that represent a number (float), including positive and negative numbers, integers, and numbers with decimal points and exponents.

To use the is_float() function, simply pass a string as an argument, and it will return True if the string is a number (float), and False otherwise.

				
					>>> is_float("3.14")
True

>>> is_float("-2.71828")
True

>>> is_float("42")
True

>>> is_float("3e8")
True

>>> is_float("hello world")
False

Checking if a string is a number (float) in Python is a common task that can be accomplished using regular expressions. The isnumeric() and isdecimal() methods are not sufficient for this task, as they only work for strings that contain digits. By using regular expressions, we can match a pattern that represents a number, and determine if a given string is a number (float) or not.

We hope that this article has been helpful to you in understanding how to check if a string is a number (float) in Python.


Thanks for reading. Happy coding!