How to print string and show canvas in the same notebook cell

Question

While working in a jupyter notebook with ipycanvas I faced the issue of printing stuff and show a canvas at the same time.

Either printing is working or the display of the canvas, but both won't.

Is there a way to do both in the same cell?

from ipycanvas import Canvas, hold_canvas

canvas = Canvas(width=600, height=600)
canvas.fill_style = '#584f4e'
canvas.fill_rect(0, 0, 600, 600)



objects_to_draw = []
class Square_obj():
    def __init__(self, x,y, width=100, height=40):
        self.x = x
        self.y = y
        self.width = width
        self.height = height
        self.selected = False
        objects_to_draw.append(self)
        
        
        
    def set_x_y(self,x_in,y_in)  :
        self.x = x_in
        self.y = y_in
    
    def draw(self):
        
        canvas.fill_style = '#38a8a4'
        canvas.fill_rect(self.x - (self.width*0.5), self.y - (self.height) , self.width, self.height)
        if self.selected:
            canvas.fill_style = '#9dcea6'
        else:
            canvas.fill_style = '#dee7bc'
        canvas.fill_rect(self.x - (self.width*0.5), self.y - (self.height*0.5) , self.width, self.height)

        
        
    def is_selected(self,x_in, y_in):
        x_coord = self.x - (self.width*0.5)
        y_coord = self.y - (self.height*0.5)

        if x_in > x_coord and x_in < (x_coord+ self.width) and  y_in > y_coord  and y_in < (y_coord  + self.height):
            
            self.set_selected(True)
            return True
        else:
            self.set_selected(False)
            return False
    
    def set_selected(self,state):
        self.selected = state


def canvas_restart():
    canvas.clear()
    canvas.fill_style = '#584f4e'
    canvas.fill_rect(0, 0, 600, 600)



def handle_mouse_down(x, y):
    print("Testing")
    if [o for o in objects_to_draw if o.selected]:
        [o.set_selected(False) for o in objects_to_draw if o.selected]
        return False
    
    
    check_bool_pos = list(set([check_region.is_selected(x,y) for check_region in objects_to_draw]))
    if len(check_bool_pos)== 1:
        if check_bool_pos[0] == False:  
            s = Square_obj(x,y)
            s.set_selected(False)
            s.draw()
            
        else:
            canvas_restart()
            [o.draw() for o in objects_to_draw]
            
            
    if len(check_bool_pos)== 0:
        s = Square_obj(x,y) 
        s.set_selected(False)
        s.draw()
    

def handle_mouse_move(x, y):    
    if [o for o in objects_to_draw if o.selected]:
        with hold_canvas(canvas):
            [o for o in objects_to_draw if o.selected][-1].set_x_y(x,y)
            canvas_restart()
            [o.draw() for o in objects_to_draw]


    
    
canvas.on_mouse_down(handle_mouse_down)
canvas.on_mouse_move(handle_mouse_move)


canvas

This is basically the example code from here. Executing the cell this way shows the canvas properly, but the test message is missing. If I manually call the handle_mouse_down() function it will be printed.

Since I'm currently using a more complicated version of this example notebook, I'd like to see error / debugging messages while using the canvas.

Answer 1

I'm using Ipycanvas + Ipywidgets together in the same project, so I usually use the Ipywidgets Output to debug. You can do something like:

from ipycanvas import Canvas, hold_canvas
from ipywidgets import Output

canvas = Canvas(width=600, height=600)
canvas.fill_style = '#584f4e'
canvas.fill_rect(0, 0, 600, 600)
debug_output = Output(layout={'border': '1px solid black'})


objects_to_draw = []
class Square_obj():
    def __init__(self, x,y, width=100, height=40):
        self.x = x
        self.y = y
        self.width = width
        self.height = height
        self.selected = False
        objects_to_draw.append(self)
        
        
        
    def set_x_y(self,x_in,y_in)  :
        self.x = x_in
        self.y = y_in
    
    def draw(self):
        
        canvas.fill_style = '#38a8a4'
        canvas.fill_rect(self.x - (self.width*0.5), self.y - (self.height) , self.width, self.height)
        if self.selected:
            canvas.fill_style = '#9dcea6'
        else:
            canvas.fill_style = '#dee7bc'
        canvas.fill_rect(self.x - (self.width*0.5), self.y - (self.height*0.5) , self.width, self.height)

        
        
    def is_selected(self,x_in, y_in):
        x_coord = self.x - (self.width*0.5)
        y_coord = self.y - (self.height*0.5)

        if x_in > x_coord and x_in < (x_coord+ self.width) and  y_in > y_coord  and y_in < (y_coord  + self.height):
            
            self.set_selected(True)
            return True
        else:
            self.set_selected(False)
            return False
    
    def set_selected(self,state):
        self.selected = state


def canvas_restart():
    canvas.clear()
    canvas.fill_style = '#584f4e'
    canvas.fill_rect(0, 0, 600, 600)


@debug_output.capture(clear_output=False)
def handle_mouse_down(x, y):
    print("Testing")
    if [o for o in objects_to_draw if o.selected]:
        [o.set_selected(False) for o in objects_to_draw if o.selected]
        return False
    
    
    check_bool_pos = list(set([check_region.is_selected(x,y) for check_region in objects_to_draw]))
    if len(check_bool_pos)== 1:
        if check_bool_pos[0] == False:  
            s = Square_obj(x,y)
            s.set_selected(False)
            s.draw()
            
        else:
            canvas_restart()
            [o.draw() for o in objects_to_draw]
            
            
    if len(check_bool_pos)== 0:
        s = Square_obj(x,y) 
        s.set_selected(False)
        s.draw()
    
@debug_output.capture(clear_output=False)
def handle_mouse_move(x, y):    
    if [o for o in objects_to_draw if o.selected]:
        with hold_canvas(canvas):
            [o for o in objects_to_draw if o.selected][-1].set_x_y(x,y)
            canvas_restart()
            [o.draw() for o in objects_to_draw]
    
    
canvas.on_mouse_down(handle_mouse_down)
canvas.on_mouse_move(handle_mouse_move)


display(canvas)
debug_output