Why this AttributeError?

Question

I'm very new to Python and I was trying to use a nice library (audiotools) to play an mp3 playlist, just as an exercise.

This is the class to play the tracklist (loosely based on THIS, once I discovered there is a "callback function with no arguments which is called by the player when the current track is finished" (*) ):

class Trackplay:
 def __init__(self,
 track_list,
 audio_output=audiotools.player.open_output('ALSA'),
 replay_gain=audiotools.player.RG_NO_REPLAYGAIN):
 self.track_index = INDEX - 1
 self.track_list = track_list
 self.player = audiotools.player.Player(
 audio_output,
 replay_gain,
 self.next_track())
 def next_track(self):
 try:
 self.track_index += 1
 current_track = self.track_list[self.track_index]
 print str(current_track)
 audio_file = audiotools.open(current_track)
 self.player.open(audio_file) # <---------- error
 self.player.play()
 except IndexError:
 print('playing finished')

Then I'm calling:

tp = Trackplay(get_track_list(PATH))

where get_track_list is a method returning a list of mp3s from the dir PATH.

The error I get (at the line marked with the "error" comment) is:

AttributeError: Trackplay instance has no attribute 'player'

I don't understand what's happening ...but reading all the AttributeError questions here, must be something stupid...

player seems to me exactly a Trackplay's attribute. Other attributes, as track_index and track_list seems OK, since the line print str(current_track) prints the current track.

Thanks for any help.

• Abdennour TOUMI: What is your OS ?
• dentex: Tried both on the Rapsberry Pi with Raspbian and the laptop with Linux Mint. Python version is 2.7.12

Answer 1

See this code here?

self.player = audiotools.player.Player(
 audio_output,
 replay_gain,
 self.next_track())

As part of creating the Player you're going to assign to self.player, you call self.next_track(). self.next_track tries to use self.player, before self.player exists!

def next_track(self):
 try:
 self.track_index += 1
 current_track = self.track_list[self.track_index]
 print str(current_track)
 audio_file = audiotools.open(current_track)
 self.player.open(audio_file)
 self.player.play()
 except IndexError:
 print('playing finished')

next_track doesn't even return anything, so it's baffling why you're trying to pass self.next_track() as an argument to Player.

Was that supposed to be a callback? If so, you should pass self.next_track to Player without calling it.

self.player = audiotools.player.Player(
 audio_output,
 replay_gain,
 self.next_track)
# ^ no call parentheses

• dentex: BINGO! I removed the parentheses and then called a self.next_track() with the parentheses (as a method) afterwards and it works... One song after the other... thank you sooo much. I understand what you say about the calling before the player even exists... now it's clear... I said it in the Q, noob error - well, actually two: the parentheses for the callback and the call before assignment - COOL. :)