MP3 player for Linux
import curses
import pygame

pygame.mixer.init(frequency=22050, size=-16, channels=2, buffer=4096)
player = pygame.mixer.music


When giving modules a shorter name, the usual method is from pygame.mixer import music as player It makes it a little clearer what you are doing.

song = "testshort.mp3"
player.load(song)
player.play()


For anything but a quick script, its recommended that you put your code inside a main function.

screen = curses.initscr()


I recommend that you take a look at the curses.wrapper function. It'll take care of closing curses correctly in the case of an error.

curses.noecho()
curses.mousemask(curses.ALL_MOUSE_EVENTS)
screen.keypad(1)
curses.curs_set(0)
screen.resize(6, 30)
screen.border(0)
screen.addstr(4, 19, "*"*5+"-"*5)
player.set_volume(0.5)
screen.addstr(4, 2, "|")


Your code jumps between curses settings, outputing to the screen, and setting up the player. I recommend dividing it cleanly between these three different tasks.

paused = 0
curses.halfdelay(1)

while True:
            busycheck = player.get_busy()
            if busycheck == 0:


use if not player.get_busy(). Using == to check in the case of bools is considered bad practice. And there is no reason to split across two lines here

                screen.addstr(4, 2, "&gt;")
            char = screen.getch()            
            if char == curses.KEY_MOUSE:
                cords = list(curses.getmouse())


There is no reason to call list here.

                mouse_x = cords[1]
                mouse_y = cords[2]


I suggest mouse_x, mouse_y = coords[:2]

                vol_on = mouse_x - 18
                vol_off = 10 - vol_on
                screen.border(0)


Why are you calling screen.border here?

                if mouse_y == 4:
                    if 29 &gt; mouse_x &gt; 18:
                        vol_bar = screen.addstr(4, 19, "*"*vol_on+"-"*vol_off)


You are basically repeating what you had previously. I suggest refactoring so as to share code.

                        volchange = (mouse_x-19)/9.0
                        player.set_volume(volchange)


See how you are effectively changing the same piece of information three times? This suggests you should put all of that in a function.

                    elif mouse_x == 2:
                        if paused == 0:
                            if busycheck == 1:
                                screen.addstr(4, 2, "&gt;")
                                player.pause()
                                paused = 1
                            else:
                                player.play()
                                paused = 0
                                screen.addstr(4, 2, "|")
                        else:
                            player.unpause()
                            screen.addstr(4, 2, "|")
                            paused = 0


Again, your code tangles together in a seeming haphazard manner the different things it does. 

This is how I'd do it:

import curses
import pygame
from pygame.mixer.music import music

SONG = "testshort.mp3"

class MusicPlayer(object):
    def __init__(self):
        pygame.mixer.init(frequency=22050, size=-16, channels=2, buffer=4096)
        music.load(SONG)
        music.play()
        self.paused = False
        self.change_volume(5)

    def change_volume(self, volume):
        self.volume = volume
        music.set_volume( volume / 9.0 )

    def toggle_pause(self):
        self.paused = not self.paused:
        if self.paused:
            music.pause()
        else:
            music.unpause()


def update_screen(screen, player):
    screen.addstr(4, 19, "*" * player.volume + "-"* (10 -player.volume))

    if music.get_busy() or player.paused:
        screen.addstr(4, 2, "|")
    else:
        screen.addstr(4, 2, "&gt;")


def main(screen):
    curses.mousemask(curses.ALL_MOUSE_EVENTS)
    screen.keypad(1)
    curses.curs_set(0)
    screen.resize(6, 30)
    screen.border(0)
    curses.halfdelay(1)

    player = MusicPlayer()

    while True:
        update_screen(screen, player)

        char = screen.getch()            
        if char == curses.KEY_MOUSE:
            mouse_x, mouse_y = curses.getmouse()[:2]
            if mouse_y == 4:
                if 29 &gt; mouse_x &gt; 18:
                    player.change_volume(mouse_x - 18)
            elif mouse_x == 2:
                player.toggle_pause()

if __name__ == '__main__':
    curses.wrapper(main)


See how each piece of the code worries about one small thing? We don't mix controlling the music with updating the display.