Why is the 'in' Operator failing

Question

I'm trying to write a function that checks if a web server is up. I run a wget command then check the result for 200 OK in the string. I'm using the in operator but it keeps failing and I'm not sure what I'm doing wrong.

I have posted my code below.

Thanks for reading.

import subprocess

web_address = "reddit.com"
wget = subprocess.Popen(["wget", "--spider", web_address], stdout=subprocess.PIPE)
output, err = wget.communicate()
response = output.decode('utf-8')
if '200 OK' in response:
    print("its up")
else:
    print("its down")

Edit: subprocess.getoutput() solved my problem.

How is it failing? What is your expected result and what result are you getting? — AChampion, Apr 08 '19 at 19:31
You should use the [`requests`](http://docs.python-requests.org/en/master/) library to make your web request instead of `wget`. — Boris Verkhovskiy, Apr 08 '19 at 19:31
@AChampion I'm expecting `its up` to be printed but `its down` keeps being printed. — user252836, Apr 08 '19 at 19:33
Try putting `print(repr(response))` before the `if` statement, to see what exactly it is. — wjandrea, Apr 08 '19 at 19:37
@Boris why? Probably the OP requires the behavior defined by the `--spider` option. This is not an unreasonable way of getting that. — juanpa.arrivillaga, Apr 08 '19 at 19:39
What makes you sure that it's the `in` operator that is failing? Please extract a [mcve] to make sure that your findings are repeatable and that your interpretation is accurate! — Ulrich Eckhardt, Apr 08 '19 at 19:39
Possible duplicate of [Running shell command and capturing the output](https://stackoverflow.com/questions/4760215/running-shell-command-and-capturing-the-output) — Boris Verkhovskiy, Apr 08 '19 at 19:44

AChampion · Answer 1 · 2019-04-08T23:47:37.277

wget logs all messages to stderr, you can capture the stderr output using stderr=subprocess.PIPE and then check err, or you can redirect stderr to stdout with stderr=subprocess.STDOUT and continue using output, e.g.:

In []:
wget = subprocess.Popen(["wget", "--spider", web_address], stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
output, err = wget.communicate()
'200 OK' in output.decode('utf-8')

Out[]:
True

Or using check_output() call:

In []:
output = subprocess.check_output(["wget", "--spider", web_address], stderr=subprocess.STDOUT, encoding='utf-8')
'200 OK' in output

Out[]:
True

Or using subprocess.run() (@Boris):

In []:
output = subprocess.run(["wget", "--spider", web_address], stdout=subprocess.PIPE, stderr=subprocess.STDOUT, text=True).stdout
'200 OK' in output

Out[]:
True

Since this is python 3, you should use `subprocess.run()` instead of `check_output()` — Boris Verkhovskiy, Apr 08 '19 at 20:01
You should do `subprocess.run(..., text=True, capture_output=True).stderr` — Boris Verkhovskiy, Apr 08 '19 at 20:13

Why is the 'in' Operator failing

1 Answers1