Python def (AttributeError: 'str' object has no attribute 'read')

Question

Trying to convert the following to a def but doing something that's probably not allowed... What am I doing wrong and how could this be done better?

# Same for both
import alsaaudio
l_input = alsaaudio.PCM(alsaaudio.PCM_CAPTURE, alsaaudio.PCM_NONBLOCK, card='default')
r_input = alsaaudio.PCM(alsaaudio.PCM_CAPTURE, alsaaudio.PCM_NONBLOCK, card='default')
#

l, data = l_input.read()
if l > 0:
  # transform data to logarithmic scale
  lin_vu = (math.log(float(max(audioop.max(data, 2),1)))-log_lo)/(log_hi-log_lo)
  # Calculate value
  lin_vu = (min(max(int(lin_vu*15),0),15))
l, data = r_input.read()
if l > 0:
  # transform data to logarithmic scale
  rin_vu = (math.log(float(max(audioop.max(data, 2),1)))-log_lo)/(log_hi-log_lo)
  # Calculate value
  rin_vu = (min(max(int(rin_vu*15),0),15))

I was hoping to do something like this as I need to read 4 values, not just the two listed:

def readvu( src ):
  l, data = src.read()
  if l > 0:
    # transform data to logarithmic scale
    l_vu = (math.log(float(max(audioop.max(data, 2),1)))-log_lo)/(log_hi-log_lo)
    # Calculate value
    l_vu = (min(max(int(l_vu*15),0),15))

lin_vu = readvu( 'l_input' );
rin_vu = readvu( 'r_input' );

But that yields the mentioned error...

Answer 1

The solution is obvious: if you call readvu('l_input') , your src becomes 'l_input' and .read() ing from it will fail.

The call should be like

lin_vu = readvu(l_input)
rin_vu = readvu(r_input)

which passes the actual variables, not the strings.

Answer 2

Change of thought brought me to the following:

# Convert log scale, calculate value & max
def vu_log(data,vu_max,max_t):
  # transform data to logarithmic scale
  vu = (math.log(float(max(audioop.max(data, 2),1)))-log_lo)/(log_hi-log_lo)
  # Calculate value
  vu = (min(max(int(vu*15),0),15))
  if vu >= vu_max:
    max_t = (3 * vu_fps) # keep max for 3 seconds
    vu_max = vu
  else:
    max_t = max(0, max_t-1) # Reduce max timer by 1 until 0
  return (vu,vu_max,max_t);

# Fetch Left input VU from ALSA
l, data = l_input.read()
if l > 0:
  # Transform data to logarithmic scale and calculate value
  lin = vu_log(data,lin_max,lin_t)
  lin_vu = lin[0]  # Desired value
  lin_max = lin[1] # Maximum value (last 3 sec)
  lin_t = lin[2]   # Used for tracking age of lin_max

Constructive suggestions always welcome... :)