Create app.py

app.py

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+"""
+app.py - Simple Unit Converter Web App using Gradio
+---------------------------------------------------
+Supports: Mass, Length, Volume, Temperature.
+Beginner-friendly code with inline comments.
+
+How to run in Google Colab:
+1. !pip install -r requirements.txt
+2. !python app.py
+3. Click the "share" link generated by Gradio.
+"""
+
+import gradio as gr
+
+# --- STEP 1: Define available units and conversion logic ---
+
+# Conversion factors relative to a base unit for each category
+UNIT_MAP = {
+    "Mass": {       # base = grams
+        "kg": 1000.0,
+        "g": 1.0,
+        "mg": 0.001,
+        "lb": 453.592,
+        "oz": 28.3495,
+    },
+    "Length": {     # base = meters
+        "mm": 0.001,
+        "cm": 0.01,
+        "m": 1.0,
+        "km": 1000.0,
+        "in": 0.0254,
+        "ft": 0.3048,
+        "yd": 0.9144,
+        "mi": 1609.34,
+    },
+    "Volume": {     # base = liters
+        "mL": 0.001,
+        "L": 1.0,
+        "m³": 1000.0,
+        "cup": 0.24,
+        "pint": 0.47,
+        "gallon": 3.785,
+    },
+}
+
+# Special case: Temperature uses formulas (not multipliers)
+TEMP_UNITS = ["C", "F", "K"]
+
+# --- STEP 2: Conversion functions ---
+
+def convert_temperature(value, from_u, to_u):
+    """Convert temperature between Celsius, Fahrenheit, Kelvin."""
+    # convert input to Celsius
+    if from_u == "C":
+        c = value
+    elif from_u == "F":
+        c = (value - 32) * 5/9
+    elif from_u == "K":
+        c = value - 273.15
+    else:
+        return "Unknown unit"
+
+    # convert Celsius to target
+    if to_u == "C":
+        return c
+    elif to_u == "F":
+        return c * 9/5 + 32
+    elif to_u == "K":
+        return c + 273.15
+
+def convert_linear(value, from_u, to_u, category):
+    """Convert Mass, Length, Volume using base-unit multipliers."""
+    mapping = UNIT_MAP[category]
+    base_value = value * mapping[from_u]       # step 1: to base
+    return base_value / mapping[to_u]          # step 2: to target
+
+def convert(value, from_unit, to_unit, category):
+    """Main function used by Gradio."""
+    # --- Input validation ---
+    try:
+        val = float(value)
+    except:
+        return "❌ Please enter a numeric value."
+
+    try:
+        if category == "Temperature":
+            result = convert_temperature(val, from_unit, to_unit)
+        else:
+            result = convert_linear(val, from_unit, to_unit, category)
+    except Exception as e:
+        return f"⚠️ Error: {e}"
+
+    return f"{val} {from_unit} = {result:.4g} {to_unit}"
+
+# --- STEP 3: Define unit lists for dropdown menus ---
+UNITS_BY_CATEGORY = {
+    "Mass": list(UNIT_MAP["Mass"].keys()),
+    "Length": list(UNIT_MAP["Length"].keys()),
+    "Volume": list(UNIT_MAP["Volume"].keys()),
+    "Temperature": TEMP_UNITS,
+}
+
+# --- STEP 4: Build Gradio UI ---
+with gr.Blocks() as demo:
+    gr.Markdown("## 🔄 Simple Unit Converter")
+
+    # Row: category + unit dropdowns
+    with gr.Row():
+        category = gr.Dropdown(list(UNITS_BY_CATEGORY.keys()), value="Mass", label="Category")
+        from_unit = gr.Dropdown(UNITS_BY_CATEGORY["Mass"], label="From Unit")
+        to_unit = gr.Dropdown(UNITS_BY_CATEGORY["Mass"], label="To Unit")
+
+    # Input + button + output
+    value_input = gr.Number(value=1, label="Value")
+    convert_btn = gr.Button("Convert")
+    output = gr.Textbox(label="Result")
+
+    # --- Update dropdowns when category changes ---
+    def update_units(cat):
+        units = UNITS_BY_CATEGORY[cat]
+        return gr.update(choices=units, value=units[0]), gr.update(choices=units, value=units[1])
+
+    category.change(update_units, category, [from_unit, to_unit])
+    convert_btn.click(convert, [value_input, from_unit, to_unit, category], output)
+
+# Run app (share=True gives a public link in Colab)
+if __name__ == "__main__":
+    demo.launch(share=True)