How to create a BMI calculator web application using Python and PyWebIO?

PyWebio is a Python library that can be used to build web applications that require a simpler UI. It provides a variety of features to create a simple web browser. Anyone can use PyWebio to build simple web applications without prior knowledge of HTML and JavaScript.

This tutorial will explain two methods of creating a network to calculate BMI. Body mass index (BMI) measures body fat based on weight and height. It is commonly used to determine whether a person is underweight, normal, overweight, or obese.

Example

In this example, we define a "BMICalculator" class that contains all the methods needed to calculate and classify BMI. The ‘__init__’ method initializes the object’s properties to None.

Next, we use the "get_user_inputs()" method, which uses the "input()" function to get the user's height and weight. The 'calculate_bmi()' method then uses the formula to calculate the BMI and rounds the result to two decimal places. The ‘classify_weight_category()’ method uses if-elif-else statements to classify the user’s weight category based on the calculated BMI. The "display_results()" method uses the "put_text()" function to display the BMI and weight categories to the user.

Finally, we define the "calculate_bmi()" function, which creates an instance of the BMICalculator class, calls its methods in sequence, and displays the results to the user. This function serves as the entry point to the PyWebIO application.

from pywebio.input import input, FLOAT
from pywebio.output import put_text
class BMICalculator:
   def __init__(self):
      self.height = None
      self.weight = None
      self.bmi = None
      self.classification = None

   def calculate_bmi(self):

      # Get user's height and weight
      self.height = input("Please enter your height in meters (m):", type=FLOAT)
      self.weight = input("Please enter your weight in kilograms (kg):", type=FLOAT)

      # Calculate BMI
      self.bmi = self.weight / (self.height ** 2)

      # Determine BMI classification
      if self.bmi < 16:
         self.classification = "Severely underweight"
      elif self.bmi < 18.5:
         self.classification = "Underweight"
      elif self.bmi < 25:
         self.classification = "Normal (healthy weight)"
      elif self.bmi < 30:
         self.classification = "Overweight"
      elif self.bmi < 35:
         self.classification = "Moderately obese"
      else:
         self.classification = "Severely obese"

      # Display results to the user
      put_text("Based on your height of {}m and weight of {}kg, your BMI is {:.1f}. This means you are classified as {}.".format(self.height, self.weight, self.bmi, self.classification))
      
      # Create BMICalculator object
      bmi_calculator = BMICalculator()
      
      # Calculate BMI and display results
      bmi_calculator.calculate_bmi()

Output

When you run the above python script, it will open a new window as shown below -

Enter your height (meters) and click the "Submit" button. After clicking the Submit button, the following screen will be displayed -

Now enter your weight in kilograms and click on the "Submit" button again. After clicking the "Submit" button, the results will be displayed as follows -

Based on your height of 1.7m and weight of 65kg, your BMI is 22.5. This means you are classified as Normal (healthy weight).

Example

This is another simple way to create a bmi web application. In this example, we define the "calculate_bmi()" function that prompts the user for height and weight. It then calculates BMI using the formula weight/(height/100)^2, rounds to two decimal places, and displays the result using the "put_text()" function. Next, it uses a series of if statements to determine the weight category based on the calculated BMI.

Finally, we use the "start_server()" function to start the web application and display the BMI calculator. We then set the title of the web application to "BMI Calculator" and the text on the "Calculate" button to "Calculate BMI."

from pywebio.input import *
from pywebio.output import *
from pywebio import start_server
def calculate_bmi():
   height = input("Enter your height (in cm)", type=FLOAT)
   weight = input("Enter your weight (in kg)", type=FLOAT)
   bmi = weight / ((height/100) ** 2)
   bmi = round(bmi, 2)
   weight_category = ""
   if bmi < 18.5:
      weight_category = "underweight"
   elif 18.5 <= bmi <= 24.9:
      weight_category = "normal weight"
   elif 25 <= bmi <= 29.9:
      weight_category = "overweight"
   else:
      weight_category = "obese"
   put_text("Your BMI is: %s" % bmi)
   put_text("You have a %s" % weight_category)
   if __name__ == '__main__':
      start_server(calculate_bmi, port=80, debug=True, title="BMI Calculator", button_text="Calculate BMI")

Output

When you run the above python script, it will open a new window as shown below -

Enter your height (meters) and click the "Submit" button. After clicking the Submit button, the following screen will be displayed -

Now enter your weight in kilograms and click on the "Submit" button again. After clicking the "Submit" button, the results will be displayed as follows -

Your BMI is: 21.22
You have a normal weight

We learned that Pywebio is a powerful library for creating simple web applications. Developers can easily make web applications that require a simpler UI. It provides input/output functions to handle conversion between Python variables and web page elements, making it easy to build interactive web interfaces. One of the main advantages of PyWebIO is its ease of use. We can get started quickly by installing the library and importing the necessary functions into your Python code. PyWebIO also provides various built-in widgets such as text boxes, drop-down menus, and buttons that can be easily incorporated into web applications. It supports multiple web frameworks, including Flask, Django and Tornado, and can be easily integrated with existing Python web applications

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