Weight Tracking Python Script

import json
import os
from datetime import datetime

def lbs_to_kg(lbs):
    """Convert weight from pounds to kilograms."""
    return lbs * 0.453592

def validate_date(date_str):
    """Validate date input and return a date object if valid."""
    try:
        return datetime.strptime(date_str, "%Y-%m-%d").date()
    except ValueError:
        return None

# Load existing entries from the JSON file
if os.path.exists("weight_log.json"):
    with open("weight_log.json", "r") as f:
        entries = json.load(f)
else:
    entries = []

# Ask the user what they want to do
action = input("Do you want to (1) record a new weight or (2) look up a past weight? Enter 1 or 2: ").strip()

if action == "1":
    # Record a new weight
    while True:
        try:
            weight = float(input("Enter your weight in pounds: "))
            break
        except ValueError:
            print("Invalid input. Please enter a number.")
    
    now = datetime.now()
    date_str = now.strftime("%Y-%m-%d")
    time_str = now.strftime("%H:%M:%S")
    
    if len(entries) > 0:
        previous_weight = entries[-1]["weight_lbs"]
        diff = weight - previous_weight
    else:
        diff = None
    
    new_entry = {"date": date_str, "time": time_str, "weight_lbs": weight}
    entries.append(new_entry)
    
    with open("weight_log.json", "w") as f:
        json.dump(entries, f, indent=4)
    
    print(f"Weight recorded: {weight:.2f} lbs ({lbs_to_kg(weight):.2f} kg)")
    
    if diff is not None:
        if diff > 0:
            print(f"You gained {diff:.2f} lbs ({lbs_to_kg(diff):.2f} kg) since the last entry.")
        elif diff < 0:
            print(f"You lost {-diff:.2f} lbs ({-lbs_to_kg(diff):.2f} kg) since the last entry.")
        else:
            print("No change in weight since the last entry.")
    else:
        print("This is your first entry. No previous data to compare.")

elif action == "2":
    # Look up a past weight
    if not entries:
        print("No weight entries found. Please record a weight first.")
    else:
        while True:
            date_input = input("Enter the date to look up (YYYY-MM-DD): ")
            lookup_date = validate_date(date_input)
            if lookup_date:
                break
            else:
                print("Invalid date format. Please enter the date in YYYY-MM-DD format.")
        
        # Find entries for the specified date
        matching_entries = [entry for entry in entries if entry["date"] == date_input]
        
        if matching_entries:
            print(f"\nWeight entries for {date_input}:")
            for entry in matching_entries:
                weight = entry["weight_lbs"]
                time = entry["time"]
                print(f"- {time}: {weight:.2f} lbs ({lbs_to_kg(weight):.2f} kg)")
        else:
            print(f"No weight entries found for {date_input}.")
else:
    print("Invalid choice. Please run the script again and enter 1 or 2.")