How I can invoke importing class in other class Python - python-2.7

Question

#!/usr/bin/env python
from __future__ import print_function
import sys
import time
import getopt
import alsaaudio
import numpy
from time import sleep
class A_weight():
def __init__(self):
skaler = 2.361E-14
fix_cur = 0.20565360419770495
A = []
hPa = 4e-11
card = 'default'
array_float = numpy.dtype(float)
stream = alsaaudio.PCM(alsaaudio.PCM_CAPTURE, alsaaudio.PCM_NORMAL, card)
stream.setchannels(1)
stream.setrate(48000)
stream.setformat(alsaaudio.PCM_FORMAT_S16_LE)
stream.setperiodsize(128)
def A(f):
return (12200**2*f**4/((f**2+20.6**2)*(f**2+12200**2)*numpy.sqrt(f**2+107.7**2)*numpy.sqrt(f**2+737.9**2)))+fix_cur
def listen(self):
glob_leq = 0
liczba_ramek = 0
index_ramek = 0
while True:
try:
l, data = stream.read()
except IOError, e:
error_count += 1
print(" (%d) Error recording: %s" % (error_count, e))
else:
if l==128:
decoded_block = numpy.frombuffer(data, dtype='int16' )
else:
continue
Y = numpy.fft.fft(decoded_block) # fft computing and normalization
Aw = A(numpy.arange(20.,20000,(19980./len(Y))))
Na = Aw*Y
inverse = numpy.fft.ifft(Y)
maks = 32768
array_float = numpy.divide(inverse.real ,float( maks))
array_float = array_float**2
sum_array = numpy.sum(array_float, dtype=float)
glob_leq = glob_leq + sum_array
liczba_ramek += 1
index_ramek += 1
if index_ramek == 375:
index_ramek=0
cis_chwil = numpy.divide(glob_leq, liczba_ramek * 128)
leq =10*numpy.log10(numpy.divide(cis_chwil, hPa))
print (leq)
#A.append(leq)
#print(max(A))
A_weight().listen()
So i trying writing program compute sound pressure level with weighting A.
All work correct but when i want close may code in class I have problem. Because something wrong with invoke to importing class in this case is it alsaaudio.
I get this feedback:
Traceback (most recent call last):
File "rec_A.py", line 64, in <module>
A_weight().listen()
File "rec_A.py", line 37, in listen
l, data = stream.read()
NameError: global name 'stream' is not defined
Do you have any idea

Answer 1

Change each occurrence of stream to self.stream:
class A_weight():
def __init__(self):
skaler = 2.361E-14
fix_cur = 0.20565360419770495
A = []
hPa = 4e-11
card = 'default'
array_float = numpy.dtype(float)
self.stream = alsaaudio.PCM(alsaaudio.PCM_CAPTURE, alsaaudio.PCM_NORMAL, card)
self.stream.setchannels(1)
self.stream.setrate(48000)
self.stream.setformat(alsaaudio.PCM_FORMAT_S16_LE)
self.stream.setperiodsize(128)
...
def listen(self):
glob_leq = 0
liczba_ramek = 0
index_ramek = 0
while True:
try:
l, data = self.stream.read()
...
This will make it an instance variable, and all other methods of that class (as long as they are passed the self argument) will have access to it through self.stream. See this bit of documentation for more details on instance variables.
Also, this is merely an aesthetic point, but the convention in Python is to use upper camel case for class names, i.e., AWeight instead of A_weight - but this will not affect how your code runs.