Snake game in Python with tkinter

Question

I created snake as my first program with GUI, I didn't learn OOP yet, so my program has no classes. I know that I should use comments, I am sorry.

Short instruction:
l - increase snake speed
k - decrease snake speed
space - pause/start/restart game it depends
a - turn snake left
d - turn snake right

What can I improve?

edit: Python version 3.6

from tkinter import *
from random import randrange

root = Tk()
root.geometry('604x604+300+100')
root.title('Snake')

c = Canvas(root,bg='black', width=604, height=604, highlightthickness=0)
c.pack()
c.create_text(302, 250, font='Terminal 30 bold', text="Press space to start", fill='white')

s = []
directions = [[-30,0],[0,-30],[30,0],[0,30]]
which_direction = randrange(0,4)
ap = []
run = True
score = 0
speed = 50
score_board = ''
pause_text = ''
sp = ''


def create_s_square(x, y):
    square = c.create_rectangle(x, y, x+30, y+30, fill='', outline='white')
    s.insert(0,square)


def create_s():
    for x in range(3):
        create_s_square(x=300,y=300)


def s_move():
    iswall()
    if run:
        for part in range(len(s)-1):
            c.coords(s[part],c.coords(s[part+1]))
        c.move(s[len(s)-1],directions[which_direction][0],directions[which_direction][1])
    is_snake()
    if run:
        aple()  
        c.after(speed*3+70,s_move)


def is_snake():
    for part in range(len(s)-1):
        if c.coords(s[part]) == c.coords(s[len(s)-1]):
            game_over()


def iswall():
    if (c.coords(s[len(s)-1])[0]+directions[which_direction][0]>=600 or \
       c.coords(s[len(s)-1])[1]+directions[which_direction][1]>=600 or \
       c.coords(s[len(s)-1])[0]+directions[which_direction][0]<=-30 or \
       c.coords(s[len(s)-1])[1]+directions[which_direction][1]<=-30) and run:
        game_over()


def aple():
    global score
    x, y = randrange(0,600,30), randrange(0,600,30)
    if not ap:
        apple = c.create_rectangle(x+7,y+7,x+23,y+23, fill='', outline='white')
        ap.append(apple)
    ap_co = [c.coords(ap[0])[0]-7,c.coords(ap[0])[1]-7]
    if c.coords(s[len(s)-1])[:2] == ap_co:
        create_s_square(c.coords(s[0])[0],c.coords(s[0])[1])
        c.delete(ap[0])
        del ap[0]
        score += 1
        score_counter()


def score_counter():
    global score_board
    c.delete(score_board)
    score_board = c.create_text(5, 25, font='Terminal 50 bold', text=str(score), fill='white', anchor=W)


def game_over():
    global run
    run = False
    c.create_text(302, 200, font='Terminal 50 bold', text='GAME OVER', fill='white')
    c.create_text(302, 260, font ='Terminal 25', text="Press space to restart", fill='white')
    root.bind('<space>', restart)


def restart(_):
    global s, ap, run, which_direction, score
    root.bind('<space>', pause)
    c.delete(ALL)
    score = 0
    score_counter()
    show_speed()
    s = []
    ap = []
    which_direction = randrange(0,4)
    create_s()
    run = True
    s_move()


def pause(_):
    global run, pause_text
    if run == False:
        run = True
        c.delete(pause_text)
        c.after(speed*3+70,s_move)
    else:
        run = False
        pause_text = c.create_text(302, 250, font='Terminal 30 bold', text="Press space to resume", fill='white')


def rotate_left(_):
    global which_direction
    if run: which_direction += 1
    if which_direction == 4: which_direction = 0


def rotate_right(_):
    global which_direction
    if run: which_direction -= 1
    if which_direction == -1: which_direction = 3   


def show_speed():
    global sp
    c.delete(sp)
    sp = c.create_text(10, 585, font='TimesNewRoman 10', text=f'speed: {100-speed}', fill='white', anchor=W)


def increase_speed(_):
    global speed
    if speed > 0:
        speed -= 1
        show_speed()

def decrease_speed(_):
    global speed
    if speed < 100:
        speed += 1
        show_speed()


def start(_):
    global score_board
    root.bind('<space>', pause)
    root.bind('k',decrease_speed)
    root.bind('l',increase_speed)
    c.delete(ALL)
    score_counter()
    show_speed()
    root.bind('a',rotate_right)
    root.bind('d',rotate_left)
    create_s()
    s_move()

root.bind('<space>',start)

root.mainloop()

Answer 1

Let's start with readability. Without deducing from functionality, I have no idea what variables like s and ap, or what functions like create_s() and s_move() do. Use clear and obvious names; the common saying is that you would read a piece of code way more often than it is written, and it thus needs to be easy to understand---you might be surprised how little even your own code will make sense to you only days after having written it.

You should also take care in how you set up lines, and sometimes more cases are worth it simply since they make it easier to follow what's happening. Your function here:

if (c.coords(s[len(s)-1])[0]+directions[which_direction][0]>=600 or \
   c.coords(s[len(s)-1])[1]+directions[which_direction][1]>=600 or \
   c.coords(s[len(s)-1])[0]+directions[which_direction][0]<=-30 or \
   c.coords(s[len(s)-1])[1]+directions[which_direction][1]<=-30) and run:

takes a bit of effort to decipher.

You also shouldn't use the same variable for different things, like this:

def create_s():
    for x in range(3):
        create_s_square(x=300,y=300)

where the x in your for loop has nothing to do with the square dimensions. Usually people would write for _ in range(3): here to show that we don't actually care about the index of the iterator.

I think you should start looking at OOP pretty soon, but before that a glaring issue is that your functions all rely entirely on "side-effects"; they don't accept any arguments and they return nothing. You should stop using global variables and instead pass whatever variables you need between your functions. Global variables are almost always a bad idea.