Python reading a not blank .txt file results with a blank line

Question

I have this code:

outtxt = "output2.txt"
command = f"ffprobe -v error -select_streams v:0 -show_entries stream=nb_frames -of default=nokey=1:noprint_wrappers=1 {inputpath}"
with open(outtxt, "w") as output:
    subprocess.Popen(command, stdout=output, stderr=output, text=True, creationflags=0x08000000)
    output.close()

with open(outtxt, "r") as file:
    data = file.read()
print(data)

When I run this, Python only prints a blank line. ("") But there is definitely a file like that and it has a single line content that stores a video file's frame count. 813 But python can't read that line. How can I read the frame count and convert to an integer? (I am on Windows 10)

Edit: Sorry for indentation. I fixed the indentation and wrote my full code. Also, i tried to close the first file but that also didn't work. I checked output2.txt and it is not empty. I deleted and tried again and it was not empty.

Please, post [mre], fix the indentation of your snippet, what `command` is, etc. — buran, Mar 02 '21 at 13:09
Also is the indentation correct? If so, you are opening the same file while it's already open. That could be an issue. — Yevhen Kuzmovych, Mar 02 '21 at 13:09
You don't need to `output.close()` when you use `with`. Just a note — Yevhen Kuzmovych, Mar 02 '21 at 13:19
Sorry for not posting enough content. I fixed the indentation and my `command` variable. And also tried to close the file before opening it again but it didn't work. @YevhenKuzmovych @buran — Nande, Mar 02 '21 at 13:20
And I checked output2.txt and yes, there is a number. output2.txt is not empty. — Nande, Mar 02 '21 at 13:21

score 1 · Accepted Answer · answered Mar 02 '21 at 13:22

Popen() merely starts a process. You will need to .communicate() and/or .wait() for it ... or, much better, use subprocess.run() which takes care of these minutiae on your behalf.

outtxt = "output2.txt"
command = f"ffprobe -v error -select_streams v:0 -show_entries stream=nb_frames -of default=nokey=1:noprint_wrappers=1 {inputpath}"
with open(outtxt, "w") as output:
    subprocess.run(command, stdout=output, stderr=output, text=True, creationflags=0x08000000)

As noted in comments already, the with statement takes care of closing the file for you, so there is no need to explicitly .close() it.

Python reading a not blank .txt file results with a blank line

1 Answers1