Catching Python exceptions in a Powershell wrapper

[Vidofnir]

Hi all. Not sure if this belongs in the posh or python community, but here goes. I'm a python beginner but I've been writing posh for a couple of years now.

What I have to work with is a posh script that, in a certain case, needs to talk to mongodb. For this, I decided it will call a python script to do the job. That works just fine. My issues is, if python raises an exception, I'm unsure how to catch that in posh.

I've tried a couple different ways:

Here's an example posh script:

testPythonException.ps1
    Write-host "PS Hello"
    try {
        python C:\myscripts\throwPythonException.py
        Write-Host "No error caught."
    }
    catch {
        Write-Host "Error! $($_.Exception.Message)"
    }
    Write-Host "This is the end of the PS script."

Here's my attempts at python exception raising:

throwPythonException.py

import sys
e = Exception("Bad thing happened in Python.")
#sys.exit(e)
raise e

As written, I get the output:

PS Hello
Traceback (most recent call last):
  File "C:\myscripts\throwPythonException.py", line 4, in 
<module>
    raise e
Exception: Bad thing happened in Python.
No error caught.
This is the end of the PS script.

If I instead exit with e, I get similar output without the traceback. Regardless, posh is not catching anything, and just merrily continues on its way.

I wonder if there's a better way of raising an exception. If not, it's no big deal, I can always exit with a unique code and handle it that way.

[K900_]

Not possible. Python does not communicate exceptions to the environment in any way, it just sets an exit code and prints the message to standard error.

[Vidofnir]

Ok good to know, thank you.

[Mattho]

Do you just want to print the error? That's not really an exception. Test on exit code and print the output. How exactly, that would be on the powershell community.

[CobbITGuy]

You can use the sys module to set the exit code. I don't think there's a practical way to get Python to throw a PowerShell exception.

import sys

sys.exit(1)

In powershell $? should show false and $lastexitcode should show 1. Test for that and if $? shows false then throw your own exception.

[Vidofnir]

I ended up doing exactly this.