turtle-graphics: I am having trouble using keys to shrink and grow the turtle

Question

I have written a code that makes a turtle move around within a box. I am trying to write a portion to change its size if you push certain keys, such as g for grow and s for shrink. However, I feel the way I make it grow and shrink is not very good. Whenever the turtle is at its default size and I press shrink, I get an error stating that its stetch_len/stretch_wid must not be 0.

I have tried using if to make it so it can't shrink if its size is one, but I cannot get it to work. I think it may have something to do with my method of shrinking it, but I am not sure.

Semi-related, I had a button I set to reset the turtle to its default when pushed. However, If I make the turtle grow bigger, it it will not shrink down as much. The larger I make it, the bigger its default seems to become. Again, I think its related to the method I used to change the size, but I am not sure.

import turtle
import os

#Creates the window for the game
wn = turtle.Screen()
wn.bgcolor("cyan")
wn.title("Game Test")

#Creates the background for the game
border_pen = turtle.Turtle()
border_pen.speed(0)
border_pen.color("black")
border_pen.penup()
border_pen.setposition(-250,-250)
border_pen.pendown()
border_pen.pensize(1)
for side in range(4):
    border_pen.fd(500)
    border_pen.lt(90)
border_pen.hideturtle()

#Creates the turtle
player = turtle.Turtle()
player.color("black")
player.shape("square")
player.pensize(2)
#player.penup()
player.setposition(0, 0)
player.setheading(90)
player.shapesize(1)

playerspeed = 10



# This resets the player to its default, beginning state
def reset():
    player.setposition(0, 0)
    player.setheading(90)
    player.shapesize(1)


# Makes the character grow larger
def grow():
    size = player.turtlesize()
    increase = tuple([1 + num for num in size])
    player.turtlesize(*increase)
    return

#Makes the character shrink
def shrink():
    size = player.turtlesize()
    decrease = tuple([-1 + num for num in size])
    if player.turtlesize() == 1:
        return
    else:
        player.turtlesize(*decrease)
    return

# Prints the characters coordinates in a seperate window from the game
def place():
    b, c = player.pos()
    print("\n")
    print(b, ",", c)


# These are the keys you push to activate different things
# The movement uses a number pad, which make programming diagonal keys easier.
turtle.listen()
turtle.onkeypress(reset, "5")
turtle.onkey(grow, "g")
turtle.onkey(shrink, "s")
turtle.onkey(place, "p")


input("Press any key to exit...")

Answer 1

Uriya Harpeness brought to my attention I was using turtlesize. I switched this to shapesize which allowed me to correct the code.

To fix the problem, I used shapesize and set the variable to a, b, c instead of size. This allowed me to just add to each one, then set the new values as the shapesize.

It also meant for the reset function, I just had to write player.shapesize(1, 1, 1).

#Makes the character shrink
def shrink():
    a, b, c = player.shapesize()
    if a > 1:
        a = a - 1
        b = b - 1
        c = c - 1
        player.shapesize(a, b, c)
        print(a, b, c)
    else:
        print(a, b, c)
        return