python - Can't seem to call a parent class's method from the child

Question

Here is my code:

from mutagen.easyid3 import EasyID3
from mutagen import File

class MusicFile:
    """A class representing a particular music file.

    Children that are intended to be instantiated must initialize fields for
    the getters that exist in this class.
    """

    def __init__(self, location):
        self.location = location

    def getLocation():
        return self.location

    def getArtist():
        return self.artist

    def getAlbum():
        return self.album

    def getTitle():
        return self.title

###############################################################################


class LossyMusicFile(MusicFile):
    """A class representing a lossy music file.

    Contains all functionality required by only lossy music files. To date, that
    is processing bitrates into a standard number and returning format with 
    bitrate.
    """
    def __init__(self, location):
        super().__init__(location)

    def parseBitrate(br):
        """Takes a given precise bitrate value and rounds it to the closest
        standard bitrate.

        Standard bitrate varies by specific filetype and is to be set by the 
        child.
        """
        prevDiff=999999999
        for std in self.bitrates:
            # As we iterate through the ordered list, difference should be 
            # getting smaller and smaller as we tend towards the best rounding
            # value. When the difference gets bigger, we know the previous one
            # was the closest.
            diff = abs(br-std)
            if diff>prevDiff:
                return prev
            prevDiff = diff
            prev = std

    def getFormat():
        """Return the format as a string.

        look like the format name (a class variable in the children), followed 
        by a slash, followed by the bitrate in kbps (an instance variable in the 
        children). a 320kbps mp3 would be 'mp3/320'.
        """
        return self.format + '/' + self.bitrate


###############################################################################

class Mp3File(LossyMusicFile):
    """A class representing an mp3 file."""

    format = "mp3"

    # Threw a large value on the end so parseBitrate() can iterate after the end
    bitrates = (32000, 40000, 48000, 56000, 64000, 80000, 96000, 112000, 
                128000, 160000, 192000, 224000, 256000, 320000, 999999)

    def __init__(self, location):
        super().__init__(location)

        id3Info = EasyID3(location)
        self.artist = id3Info['artist'][0]
        self.album = id3Info['album'][0]
        self.title = id3Info['title'][0]
        # Once we set it here, bitrate shall be known in kbps
        self.bitrate = (self.parseBitrate(File(location).info.bitrate))/1000

Now, when I try to instantiate an Mp3File , it gives me an error on the last line of Mp3File.__init__() :

line 113, in __init__
self.bitrate = (self.parseBitrate(File(location).info.bitrate))/1000
NameError: name 'parseBitrate' is not defined

However, it seems to me that it should be failing to find the method in Mp3File , and then looking for the method in the parent class, LossyMusicFile , where it does exist.

I tried changing that line to self.bitrate = (super().parseBitrate(File(location).info.bitrate))/1000 so that it would be explicitly using the parent class's method, but I get the same error. What's going on?

Apologies if this has been asked before or is a dumb question, but I couldn't find it when I searched and I am, in fact, dumb.

Answer 1

All of your instance methods must have self as the first parameter. What's happening here is that in parseBitrate() you renamed self to br . You need parseBitrate(self, br) in order to accept a bitrate. You need to add self to the argument list in other methods like getFormat() too.

1. Your code uses thisVariableNamingStyle it's against Python's offical style document, PEP 8 .
2. MusicFile doesn't inherit off of object . You can only call methods inherited from aa higher class in "new-style classes". In order to make your class "new-style", you must inherit off of object .

In addition, get an IDE like PyCharm that can automatically warn you of these errors in the future.