Calling variable within an __init__ function aren't defined in my other class methods

Question

I know this is a basic question and I have no doubt that it has been answered but I cant find any good info anywhere, so:

I have a list of methods that work wonderfully when outside of a class and when variables are declared globally. However, when I try to contain the methods and variables within a class I run into all sorts of errors concerning the variables.

class AudioFeatures(object):
def __init__(self, track, sr):
 self.track = track
 self.sr = sr 
 hop_length = 2048
 frame_length_in_seconds = 10 
 frame_length = sr*frame_length_in_seconds
 final_sample = int(librosa.get_duration(track)*sr)
 full_rms = librosa.feature.rms(track, frame_length=frame_length, hop_length=hop_length, center=True)
 std_rms = np.std(full_rms)
 rms_selection = std_rms + (std_rms-(std_rms*(1-std_rms)))
 return
def find_nearest(self, array, value):
 array = array
 idx = (np.abs(array - value)).argmin()
 return idx
def get_min_energy_sample(self, track, sr):
 min_value = np.mean(full_rms) - rms_selection
 min_value_loc = find_nearest(full_rms, min_value)
 min_energy_frame_start = librosa.frames_to_samples(min_value_loc, hop_length=hop_length)
 min_energy_frame_end = min_energy_frame_start + frame_length
 #check to make sure the frame is 10seconds long otherwise set frame to final 10 seconds
 if min_energy_frame_end > final_sample:
 min_energy_sample = track[(final_sample-frame_length): final_sample]
 else:
 min_energy_sample = track[min_energy_frame_start: min_energy_frame_end]
 return min_energy_sample
temp_track = AudioFeatures(file_loc, sr) #this works fine
temp_track.get_min_energy_sample()

when running this i am told that full_rms (which is the first variable referenced from the class in the get_min_energy_sample) is not defined. I've tried every combination of self. that I can think of. Any help would be wonderful.

• Mad Physicist: Start by fixing your indentation and posting a minimal reproducible example
• drum: to call them: self.function_name()
• chepner: rms_selection (and possible other variables) is local to __init__. If you want it available in other methods, you have to make it an instance attribute, like track and sr.

Answer 1

You need to remember to store information that you will need to use in the methods as attributes, and then reference them using self., like so:

class AudioFeatures(object):
 def __init__(self, track, sr):
 self.track = track
 self.sr = sr 
 self.hop_length = 2048
 frame_length_in_seconds = 10 
 self.frame_length = sr*frame_length_in_seconds
 self.final_sample = int(librosa.get_duration(track)*sr)
 self.full_rms = librosa.feature.rms(track, frame_length=self.rame_length, hop_length=hop_length, center=True)
 std_rms = np.std(self.full_rms)
 self.rms_selection = std_rms + (std_rms-(std_rms*(1-std_rms)))
 def find_nearest(self, array, value):
 idx = (np.abs(array - value)).argmin()
 return idx
 def get_min_energy_sample(self, track, sr):
 min_value = np.mean(self.full_rms) - self.rms_selection
 min_value_loc = find_nearest(self.full_rms, min_value)
 min_energy_frame_start = librosa.frames_to_samples(min_value_loc, hop_length=self.hop_length)
 min_energy_frame_end = min_energy_frame_start + self.frame_length
 #check to make sure the frame is 10seconds long otherwise set frame to final 10 seconds
 if min_energy_frame_end > self.final_sample:
 min_energy_sample = track[(self.final_sample-self.frame_length): self.final_sample]
 else:
 min_energy_sample = track[min_energy_frame_start: min_energy_frame_end]
 return min_energy_sample

Answer 2

@ATony is correct, but let's look at a simpler example, cut down to demonstrate the core issue.

>>> class A(object):
... def __init__(self):
... self.foo = 42
... bar = 27
... def baz(self):
... print(self.foo)
... print(bar)
... 
>>> a = A()
>>> a.baz()
42
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
 File "<stdin>", line 7, in baz
NameError: global name 'bar' is not defined
>>> 

Now compare this to the following, where both foo and bar are attributes of self. Now we can access both of them from other methods.

>>> class A(object):
... def __init__(self):
... self.foo = 42
... self.bar = 27
... def baz(self):
... print(self.foo)
... print(self.bar)
... 
>>> a = A()
>>> a.baz()
42
27
>>>