Draw an Arrow with OpenCV (and python version too)

OpenCV does not provide functions to draw an arrow. We will introduce a simple way to do it!
First, we draw a simple line (easy). Then, we plot the two segments that represent the arrow. These segments present an angle of 45 degrees (pi / 4) with the main line.
Here is the code for that:
#include <stdio.h>
#include <cv.h>
#include <highgui.h>

void drawArrow(IplImage *image, CvPoint p, CvPoint q, CvScalar color, int arrowMagnitude = 9, int thickness=1, int line_type=8, int shift=0) 
{
    //Draw the principle line
    cvLine(image, p, q, color, thickness, line_type, shift);
    const double PI = 3.141592653;
    //compute the angle alpha
    double angle = atan2((double)p.y-q.y, (double)p.x-q.x);
    //compute the coordinates of the first segment
    p.x = (int) ( q.x +  arrowMagnitude * cos(angle + PI/4));
    p.y = (int) ( q.y +  arrowMagnitude * sin(angle + PI/4));
    //Draw the first segment
    cvLine(image, p, q, color, thickness, line_type, shift);
    //compute the coordinates of the second segment
    p.x = (int) ( q.x +  arrowMagnitude * cos(angle – PI/4));
    p.y = (int) ( q.y +  arrowMagnitude * sin(angle – PI/4));
    //Draw the second segment
    cvLine(image, p, q, color, thickness, line_type, shift);
}  

//How to call this function
int main()
 {
    
   IplImage *canvas = cvCreateImage(cvSize(320, 240), IPL_DEPTH_8U, 3);
    cvNamedWindow(“win”);  
    drawArrow(canvas, cvPoint(10, 20), cvPoint(100, 150), CV_RGB(100, 0, 255), 20);
    cvShowImage(“win”, canvas);
    cvWaitKey();
    cvReleaseImage(&canvas);
    cvDestroyAllWindows();
    return 1;
}