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 a a 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.