JD Smith JD Smith - 1 year ago 344
Python Question

AttributeError: Wave_write instance has no attribute '__exit__'

While working with some code given to me by my professor to use in an assignment, I cannot change per instructions. I've been looking around and added closing around the initial write but is there to prevent modify the starter code?

The code came from:

Calling Code:

def run_menu():

global CURRENT_TIME

# Provide a minimal indication that the program has started.
print(MINIMAL_HELP_STRING)

# Get the first keystroke.
c = readchar.readchar()

# Endless loop responding to the user's last keystroke.
# The loop breaks when the user hits the QUIT_MENU_KEY.
while True:

# Respond to the user's input.
if c == FORWARD_KEY:

# Advance the time, looping back around to the start.
CURRENT_TIME += 1
if CURRENT_TIME == len(NUMBERS_WAV):
CURRENT_TIME = 0

# Concatenate three audio files to generate the message.
sound.combine_wav_files(TMP_FILE_WAV, YOU_SELECTED_WAV,
NUMBERS_WAV[CURRENT_TIME], AM_WAV)

# Play the concatenated file.
sound.Play(TMP_FILE_WAV)


Function Code:

def combine_wav_files(out_file, *files):
with wave.open(out_file, 'wb') as out:
with wave.open(files[0], 'rb') as first_in:
(nchannels, sampwidth, framerate, nframes, comptype, compname) =\
first_in.getparams()
out.setparams(first_in.getparams())
for filename in files:
with wave.open(filename, 'rb') as cur_in:
if (cur_in.getnchannels() != nchannels or
cur_in.getsampwidth() != sampwidth or
cur_in.getframerate() != framerate or
cur_in.getcomptype() != comptype or
cur_in.getcompname() != compname):
raise Exception('Mismatched file parameters: ' + filename)
out.writeframes(cur_in.readframes(cur_in.getnframes()))


Error Message:

Exception wave.Error: Error('# channels not specified',) in <bound method Wave_write.__del__ of <wave.Wave_write instance at 0x104029e60>> ignored
Traceback (most recent call last):
File "sample_menu.py", line 144, in <module>
main()
File "sample_menu.py", line 25, in main
run_menu()
File "sample_menu.py", line 113, in run_menu
NUMBERS_WAV[CURRENT_TIME], AM_WAV)
File "/Users/jaredsmith/Desktop/443/P1 Starter Code 2017/sound.py", line 86, in combine_wav_files
with wave.open(out_file, 'wb') as out:
AttributeError: Wave_write instance has no attribute '__exit__'


I put the fix under the imports and it works!

Fix (Update):

####
# From http://web.mit.edu/jgross/Public/21M.065/sound.py 9-24-2017
####

def _trivial__enter__(self):
return self
def _self_close__exit__(self, exc_type, exc_value, traceback):
self.close()

wave.Wave_read.__exit__ = wave.Wave_write.__exit__ = _self_close__exit__
wave.Wave_read.__enter__ = wave.Wave_write.__enter__ = _trivial__enter__

Answer Source

You are using a Wave_write instance inside a with statement. For it to work properly, Wave_write must be a context manager, meaning it must implement both methods __enter__() and __exit__(). That is not the case here.

You must either add the __exit__ method to Wave_write, or remove the with statement and close the input manually (if needed). Example:

out = wave.open(out_file, 'wb'):
    [do_stuff]
out.close() # if Wave_write implements a closing method, use it. the with statement and __exit__() method would have handled that for you.

See https://docs.python.org/2/reference/compound_stmts.html#with and https://docs.python.org/2/library/contextlib.html

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