In this tutorial, I will explain how to check if a string is an integer or float in Python. As a Python developer working on a project for one of my clients in New York, I came across a situation when dealing with user input and data parsing, I needed to check if a string is an integer or float. Let’s get into the details with examples and screenshots of executed example code.
Methods to Check if a String is an Integer in Python
Python provides various methods to check if a string is an integer. Let us see some important methods.
Method 1. Use the isdigit() Method
The isdigit() method is a built-in Python string method that returns True if all characters in the string are digits and there is at least one character otherwise, it returns False.
def is_integer(s):
return s.isdigit()
# Example
input_string = "12345"
print(is_integer(input_string))
input_string = "12345.67"
print(is_integer(input_string)) Output:
True
FalseI have executed the above example code and added the screenshot below.
Read How to Remove Numbers from Strings in Python?
Method 2. Use the int() Function with Exception Handling
Another approach is to use the int() function to attempt to convert the string to an integer. If the conversion fails, a ValueError is raised, which we can catch and handle.
def is_integer(s):
try:
int(s)
return True
except ValueError:
return False
# Example
input_string = "67890"
print(is_integer(input_string))
input_string = "67890.12"
print(is_integer(input_string))Output:
True
FalseI have executed the above example code and added the screenshot below.
Check out Difference Between Functions and Methods in Python
Method 3. Use Regular Expressions
Regular expressions provide a powerful way to validate strings. The re module in Python can be used to check if a string contains only digits.
import re
def is_integer(s):
return bool(re.match(r"^\d+$", s))
# Example
input_string = "54321"
print(is_integer(input_string))
input_string = "54321.89"
print(is_integer(input_string)) Output:
True
FalseI have executed the above example code and added the screenshot below.
Read How to Use the insert() Function in Python?
Methods to Check if a String is a Float in Python
Let us see some important methods to check if a string is a float in Python.
Method 1. Use the float() Function with Exception Handling
Similar to checking for integers, you can use the float() function to attempt to convert the string to a float.
def is_float(s):
try:
float(s)
return True
except ValueError:
return False
# Example
input_string = "12345.67"
print(is_float(input_string))
input_string = "12345"
print(is_float(input_string))
input_string = "12345.67.89"
print(is_float(input_string))Output:
True
True
FalseI have executed the above example code and added the screenshot below.
Check out How to Use the arange() Function in Python?
Method 2. Use Regular Expressions
Regular expressions can also be used to validate if a string is a float. The pattern for a float includes an optional sign, digits, and an optional decimal point followed by digits.
import re
def is_float(s):
return bool(re.match(r"^[+-]?(\d+(\.\d*)?|\.\d+)$", s))
# Example
input_string = "67890.12"
print(is_float(input_string))
input_string = "67890"
print(is_float(input_string))
input_string = "67890.12.34"
print(is_float(input_string))Output:
True
True
FalseCheck out How to Use the Python Pass Function?
Combine Checks for Integer and Float
In some cases, you may want to check if a string is either an integer or a float. You can combine the methods described above to create a comprehensive function.
def is_number(s):
try:
float(s)
return True
except ValueError:
return False
# Example
input_string = "12345"
print(is_number(input_string))
input_string = "12345.67"
print(is_number(input_string))
input_string = "12345.67.89"
print(is_number(input_string))Output:
True
True
FalseRead Should I Learn Java or Python?
Examples
Let us see some real-world scenarios to understand more about the topic.
Example 1: Validate User Input in a Financial Application
Think you’re developing a financial application where users input their annual income and tax rates. You need to ensure that these inputs are numeric values.
def validate_financial_input(income, tax_rate):
if not is_number(income):
return "Invalid income input. Please enter a numeric value."
if not is_number(tax_rate):
return "Invalid tax rate input. Please enter a numeric value."
return "Inputs are valid."
# Example
income = "50000"
tax_rate = "7.5"
print(validate_financial_input(income, tax_rate))
income = "50k"
tax_rate = "7.5"
print(validate_financial_input(income, tax_rate)) Output:
Inputs are valid.
Invalid income input. Please enter a numeric value.Read Difference Between {} and [] in Python
Example 2: Parse Data from a CSV File
Consider a scenario where you’re parsing a CSV file containing product prices. You need to ensure that the prices are valid floats.
import csv
def validate_prices(file_path):
with open(file_path, mode='r') as file:
csv_reader = csv.reader(file)
for row in csv_reader:
product_name, price = row
if not is_float(price):
print(f"Invalid price for product {product_name}: {price}")
else:
print(f"Valid price for product {product_name}: {price}")
# Example CSV content:
# Apple,1.25
# Banana,0.75
# Cherry,invalid_price
validate_prices('products.csv')Read Difference Between “is None” and “== None” in Python
Conclusion
In this tutorial, we explored various methods to check if a string is an integer or float in Python. By using built-in methods like isdigit(), exception handling with int() and float(), and regular expressions, you can effectively validate numeric strings in Python. We used exception handling with float() function , using regular expressions. I combined checks for integers and float with real-world examples.
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I am Bijay Kumar, a Microsoft MVP in SharePoint. Apart from SharePoint, I started working on Python, Machine learning, and artificial intelligence for the last 5 years. During this time I got expertise in various Python libraries also like Tkinter, Pandas, NumPy, Turtle, Django, Matplotlib, Tensorflow, Scipy, Scikit-Learn, etc… for various clients in the United States, Canada, the United Kingdom, Australia, New Zealand, etc. Check out my profile.
