[Tutor] Does python change subprocess based on whether it is run in the interactive shell or not

[Alan Gauld]

On 28/10/2022 12:38, Nathan Smith wrote:

>      p = subprocess.Popen(cmd, stdout=subprocess.PIPE, 
> stdin=subprocess.PIPE, stderr=subprocess.PIPE)
>      [stdout, stderr]=p.communicate(data)

The square brackets should not be needed. Unpacking
will work based on the comma alone.

> Where data is some data taken from io.bytesIO.read
> 
> And cmd is a command for ffmpeg like so:
> 
> cmd="ffmpeg/ffmpeg.exe -f wav -ac 2 -i - -f mp3 -ab 128000 - -y"

so far so good.

> When run in an interactive shell this works like a charm. When run in a 
> script file, this breaks. 

Breaks? How?
Error message? Bad data? No data?

Give us a clue.


> At first I thought it was an issue with 
> FFMPEG, but now I'm wondering if python is changing something under the 
> hood?

How are you running the script file?
Is it the same user environment as the interactive Python session
or via a cron job or similar?

> When running from a script, should I be using shell=True?

Probably not. shell=True simply says to read the command
in a shell environment expanding wildcards etc. You don't seem
to be using anything that needs shell expansion.


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Alan G
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