Flutter Python Bridge

flutter_python_bridge

pub package

A powerful Flutter library that enables running Python code directly in Flutter applications. This package provides a seamless bridge between Flutter and Python, allowing you to leverage Python's extensive ecosystem of libraries for machine learning, data analysis, image processing, and more.

Demo

🎥 Watch Demo Video

Features

  • Run Python code directly from Flutter
  • Execute Python script files
  • Install Python packages at runtime (where supported)
  • Machine Learning with scikit-learn, TensorFlow, etc.
  • Data Analysis with pandas, numpy, matplotlib
  • Image Processing with OpenCV
  • Cross-platform support with optimized implementations
  • Android optimization via Chaquopy integration

Installation

Add this to your package's pubspec.yaml file:

dependencies:
  flutter_python_bridge: ^0.2.0

Android Setup

For Android, this library uses Chaquopy to run Python code. Configure your Android project:

  1. Add the Chaquopy Gradle plugin to your app's android/build.gradle file:
buildscript {
    repositories {
        google()
        mavenCentral()
        maven { url "https://chaquo.com/maven" }
    }
    dependencies {
        classpath "com.chaquo.python:gradle:13.0.0"
    }
}
  1. Apply the Chaquopy plugin in your app-level android/app/build.gradle:
apply plugin: "com.chaquo.python"

android {
    defaultConfig {
        ndk {
            abiFilters "armeabi-v7a", "arm64-v8a", "x86", "x86_64"
        }
        python {
            version "3.8"
            pip {
                // Add your required Python packages here
                install "numpy"
                install "pandas"
                install "matplotlib"
                install "scikit-learn"
                install "opencv-python"
                install "pillow"
            }
        }
    }
}

Important Note for Android: Due to Chaquopy limitations, Python packages must be bundled at build time. Runtime installation of packages not included in the build.gradle will not work on Android.

iOS/Desktop Setup

For iOS and desktop platforms, this library uses the system Python. Ensure Python 3.6+ is installed on your development machine.

Basic Usage

Running Python Code

import 'package:flutter_python_bridge/flutter_python_bridge.dart';

// Create a Python bridge instance
final pythonBridge = PythonBridge();

// Run simple Python code
Future<void> runPythonExample() async {
  final result = await pythonBridge.runCode('''
import numpy as np

def calculate_mean(numbers):
    return np.mean(numbers)

result = calculate_mean([1, 2, 3, 4, 5])
print(f"The mean is: {result}")
''');

  if (result.success) {
    print('Output: ${result.output}');
  } else {
    print('Error: ${result.error}');
  }
}

Running a Python Script File

// Run a Python script file
Future<void> runPythonScript() async {
  final result = await pythonBridge.runScript('/path/to/script.py');

  if (result.success) {
    print('Output: ${result.output}');
  } else {
    print('Error: ${result.error}');
  }
}

Installing Python Packages

// Install a Python package (works on desktop, limited on Android)
Future<void> installPackage() async {
  final result = await pythonBridge.installPackage('matplotlib');

  if (result.success) {
    print('Package installed successfully');
  } else {
    print('Failed to install package: ${result.error}');
  }
}

Advanced Examples

Data Analysis with Pandas and Matplotlib

Future<void> runDataAnalysis() async {
  // Create a temporary directory for output files
  final tempDir = await getTemporaryDirectory();
  final outputDir = Directory(path.join(tempDir.path, 'python_output'));
  if (!await outputDir.exists()) {
    await outputDir.create(recursive: true);
  }
  
  final plotPath = path.join(outputDir.path, 'plot.png');
  
  final pythonCode = '''
import pandas as pd
import matplotlib.pyplot as plt
import numpy as np
import seaborn as sns

# Create sample data
data = {
    'Category': ['A', 'B', 'C', 'D', 'E'],
    'Values': [5, 7, 3, 9, 6]
}

# Create a DataFrame
df = pd.DataFrame(data)

# Create a plot
plt.figure(figsize=(10, 6))
sns.barplot(x='Category', y='Values', data=df)
plt.title('Sample Bar Plot')
plt.tight_layout()

# Save the plot
plt.savefig('${plotPath.replaceAll('\\', '/')}')
print(f"Plot saved to {plotPath}")

# Return some statistics
stats = df.describe().to_dict()
print(stats)
''';

  final result = await pythonBridge.runCode(pythonCode);
  
  if (result.success) {
    print('Analysis complete. Plot saved at: $plotPath');
  }
}

Machine Learning with Scikit-Learn

Future<void> runMachineLearning() async {
  final features = [5.1, 3.5, 1.4, 0.2]; // Example iris flower features
  final featuresStr = features.map((f) => f.toString()).join(', ');
  
  final pythonCode = '''
import numpy as np
from sklearn.datasets import load_iris
from sklearn.ensemble import RandomForestClassifier

# Load the Iris dataset
iris = load_iris()
X = iris.data
y = iris.target
feature_names = iris.feature_names
target_names = iris.target_names

# Train a Random Forest classifier
rf = RandomForestClassifier(n_estimators=100, random_state=42)
rf.fit(X, y)

# Make a prediction for the input features
input_features = np.array([[${featuresStr}]])  # Properly formatted as 2D array
print(f"Input features: {input_features[0]}")

# Predict the class
prediction = rf.predict(input_features)[0]
predicted_class = target_names[prediction]
print(f"Predicted class: {predicted_class}")

# Get class probabilities
probabilities = rf.predict_proba(input_features)[0]
class_probability = probabilities[prediction]
print(f"Probability: {class_probability:.4f}")
''';

  final result = await pythonBridge.runCode(pythonCode);
  
  if (result.success) {
    print('ML prediction output: ${result.output}');
  }
}

Image Processing with OpenCV

Future<void> processImage(String imagePath) async {
  final imageProcessor = ImageProcessor();
  
  // Define image operations
  final operations = [
    GrayscaleOperation(),
    BlurOperation(kernelSize: 5),
    EdgeDetectionOperation(threshold1: 100, threshold2: 200),
  ];
  
  // Process the image and save to assets folder
  final result = await imageProcessor.processImage(
    imagePath,
    operations,
    saveToAssets: true, // Save to assets folder instead of cache
  );
  
  if (result.success) {
    final processedImagePath = result.returnValue as String?;
    print('Image processed and saved to: $processedImagePath');
  } else {
    print('Error processing image: ${result.error}');
  }
}

iOS and Web Limitations

Due to platform restrictions, running Python directly within iOS apps or web applications is not possible:

iOS Limitations

iOS's sandboxing model prevents apps from:

  1. Launching external processes (like Python)
  2. Installing software at runtime
  3. Executing arbitrary code outside the app sandbox

Web Limitations

Web applications run in a browser sandbox that prevents:

  1. Direct access to the file system
  2. Launching external processes
  3. Running native code like Python

Alternatives for iOS and Web

If you need Python functionality in an iOS app or web application, consider these alternatives:

  1. Backend Service: Create a Python API backend that your app can call
  2. Feature Detection: Detect the platform and disable Python features on unsupported platforms
  3. WebAssembly (Experimental): For some use cases, libraries like Pyodide might help run Python code via WebAssembly
// Example of platform-specific code
import 'dart:io' if (dart.library.html) 'package:flutter_python_bridge/src/web_stub.dart';

// Check platform
if (Platform.isIOS || Platform.isWeb) {
  // Show alternative UI or use a backend service
} else {
  // Use Flutter Python Bridge directly
  final result = await pythonBridge.runCode(pythonCode);
}

Available Image Operations

The ImageProcessor class supports various image operations:

  • GrayscaleOperation() - Convert image to grayscale
  • BlurOperation(kernelSize: 5) - Apply Gaussian blur
  • EdgeDetectionOperation(threshold1: 100, threshold2: 200) - Detect edges using Canny algorithm
  • BrightnessContrastOperation(brightness: 30, contrast: 1.2) - Adjust brightness and contrast
  • RotateOperation(angle: 45) - Rotate image by specified angle
  • FlipOperation(horizontal: true, vertical: false) - Flip image horizontally or vertically
  • CropOperation(x: 100, y: 100, width: 300, height: 300) - Crop image to specified region
  • ResizeOperation(width: 800, height: 600) - Resize image to specified dimensions

Platform-Specific Considerations

Android

  • Uses Chaquopy for Python execution
  • Python packages must be included in the build.gradle file
  • Runtime package installation is limited to packages already included in the build

iOS/Desktop

  • Uses system Python interpreter
  • Supports runtime package installation
  • Requires Python to be installed on the system

Error Handling

All methods return a PythonResult object that contains:

  • success: Boolean indicating if the operation was successful
  • output: String containing the standard output from Python
  • error: String containing any error message (if success is false)
  • returnValue: Optional value returned from the operation

Troubleshooting

Android Issues

  • Missing Python packages: Ensure all required packages are listed in your build.gradle file
  • Runtime pip install fails: Remember that Chaquopy does not support ensurepip and runtime pip installs are limited

iOS/Desktop Issues

  • Python not found: Ensure Python 3.6+ is installed and in your PATH
  • Package installation fails: Check internet connectivity and package name spelling

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

License

This project is licensed under the MIT License - see the LICENSE file for details.

Libraries

flutter_python_bridge