How to see the outputs and logs of the a python script?

I have a pipeline which included a python script. Although the pipeline works properly but I cannot see the output of my script both in the data preview and also in the logs. E.g. when I download the logs I dont see this output:" This is a python log")

Also the data preview somehow does not work for this specific pipeline although there is no special character in the project name which apparently is a known bug.
self.output.write("This is a python output")

Any idea on this would be appreciated.

Hi @irsl ,

What do you mean by the data preview does not work ? Is there no preview available or something else ? Can you elaborate on that ? Or maybe you forgot to set the snap mode to “Validate & Execute” ?

Hi @j.angelevski,
thank you for the response. I have checked and all snaps are in “Validate & Execute” mode. But still no preview is available. After running the script 3 docs are produced as shown in the screenshot below but I cannot see them in the preview:


The python script runs a cli command to extract a compressed file in tar format. I want to customise the script but I dont see any output or any logs from the script.

To me, this looks like you are executing the pipeline. When you execute the pipeline you can’t preview the data, you need to validate to be able to preview the output data.


You can see the difference between executed and validated pipeline. The first image is executed pipeline and is colored in a dark green color. The second image is when you validate and is colored with a light green color and you can see the preview icon for each snap.

Hello @irsl! @j.angelevski is correct, your pipeline has been executed instead of validated, which means you will not see the preview output.

I have a detailed response here for anyone new to SnapLogic or new to using the Script Snap with Python, so if you’re familiar with that please skip to the TLDR; section where I have a sample pipeline and video on how the pipeline works to untar files. In the designer you’re looking for the V inside the gear, which is the middle of these three icons from the toolbar (others shown for reference:)

Once a pipeline has successfully validated that icon will become a darker icon with a check mark in it like this:

If you take the default Python Script template and replace the default self.output.write(inDoc, outDoc) with the line self.output.write("This is a python output"), the output would look like this, printed one time for each input document and without any JSON keys for reference:

I have ten records randomly generated from Mockaroo in my JSON Generator. To manipulate the JSON output from the Python Script snap I actually want to work with the ‘output’ dictionary, the one that looks like the snippet below. Since that snippet is in the while self.input.hasNext() block it is executed once for each incoming document. In other words, all it does it pass the incoming document, inDoc, through to the output under the $original key.

outDoc = {
   'original' : inDoc

Now let’s say I want to output my original document AND a custom message. Here is the snippet that shows how we can do that.

outDoc = {
   'original' : inDoc
outDoc['custom_message'] = {
   "This is Python output!"
self.output.write(inDoc, outDoc)

Since the outDoc dictionary is created for capturing $original by default, I need make sure the content I want to add is appended to it instead of overwriting it. For example, if the second statement was outDoc = {‘custom_mesage’ : “This is python output!”} I would overwrite it. Here is a screenshot of the output now:

Accessing JSON keys within a record works in a similar fashion using inDoc. Looking at the screenshot you can see my incoming document has a “first_name” key so if I wanted to run some Python on just that field, I could reference it like inDoc['first_name'].

Now let’s talk about" This is a python log") which by default in the Script Snap would be"Executing Transform script"). These messages will be written to the logs on the Snaplex node rather than in any place you can see in the Designer. If the pipeline was executed rather than validated so you can find it in the Dashboard, the little table icon in the Status column allows you to fetch the logs if they have not rolled on the node:

The files download as JSON and here is the line for the default"Executing Transform script"):

    "Process": "Script[5592aed995315c0d2e1aaeeb_4a397c14-d757-419a-84cf-5e61c056f455 -- 55bbca61-0a87-4784-b08a-92224f953f33]",
    "TimeStamp": "8/9/2021 6:50 PM",
    "RuntimeID": "5592aed995315c0d2e1aaeeb_4a397c14-d757-419a-84cf-5e61c056f455",
    "File": "",
    "Message": "Executing Transform script",
    "SnapLabel": "Script",
    "Exception": ""

If you had direct access to the logs on the Snaplex node it only looks slightly different:

    "ts": "2021-08-09T22:53:57.547Z",
    "lvl": "INFO",
    "fi": "",
    "msg": "Executing Transform script",
    "snlb": "Script",
    "snrd": "6e759256-449e-4a9a-808d-4e8702629356",
    "plrd": "5592aed995315c0d2e1aaeeb_9b2d9e11-e85d-4c76-a05a-2434fc986d6e",
    "prc": "Script[5592aed995315c0d2e1aaeeb_9b2d9e11-e85d-4c76-a05a-2434fc986d6e -- 6e759256-449e-4a9a-808d-4e8702629356]",
    "xid": "94ea29d4-9722-4f42-9774-bda0cff3ce30"

I am attaching a pipeline and link to a video that shows how the pipeline works in case you or anyone else need help with that.
Untar Pipeline: UntarFile_2021_08_09.slp (13.2 KB)
Python Script Example Pipeline: Community_PythonScriptOutput_2021_08_09.slp (14.0 KB)

1 Like

Thank you both for the help and for the detailed answers. The issue with this specific pipeline is still not solved though.

  • I always do the validation before running the pipeline (in fact each pipeline saving will automatically validate the pipeline) and still this specific pipeline does not show any data preview. This could be the result of having custom snaps specific for connecting to our internal platform to read and write data. Other pipelines which includes python scripts do not have such an issue.
  • @rsramkosk When I validate your pipeline I can see both the data preview and the python logs (via Dashboard). But for my own pipeline this is not the case. The main pipeline invokes multiple child pipelines and the logs of the parent pipeline should include the all the script logs. The python script runs some command lines in a mounted storage. Still not sure what happens to the log afterwards.
  • @rsramkosk a question/feedback on your UntarFile workflow: Could it be that pipe.tmpDir in some instances couldn’t be accessed because of the different admin configurations? When I validate/run your workflow I get this error: Failure: Error browsing the directory contents. /logs/snaplogic/tmp/sl_pipe_5e31419d06650079bd2a0fb7_5c211261-c4d8-41b5-bbaa-e054812628f3, Resolution: Please try again.

Thank you for the help.

@irsl Your observation about the custom snap is significant here as that could definitely be why you aren’t seeing any preview data from the Script Snap - if no preview data goes in, no preview data comes out (unless the Script Snap itself is making a connection to a target to pull data).

From your third point, it does sound like your temp location has been redirected to /logs/snaplogic which is not a default directory that we create, so you would have to check with your infrastructure or system administrators on that point. Our default logging location on Linux would be /opt/snaplogic/run/logs.

Considering the custom Snap, custom logging location, and temp folder location, you may need work with Support to move this situation forward unless you can post more detail here about the custom Snap, temp folder permissions, and Script Snap code.