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Error using hapi for a headless Houdini

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KatanaPoland
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Hi, I'm trying to connect to a headless Houdini in a Windows terminal to edit a hdalc or hiplc file using hapi. I'd like to create a new node inside the file for starters and I encounter an 'Invalid id' error (below).

I'm using hython.exe as my shell (I couldn't import hou/hapi/anything-Houdini after adding 'C:\Program Files\Side Effects Software\Houdini 19.5.569\houdini\python3.7libs' to my Windows environment path, I get "import _hou: ImportError: DLL load failed: The specified module could not be found" error). I've been following this Getting Started tutorial in https://www.sidefx.com/docs/houdini/hapi/ [www.sidefx.com]

Error:
Traceback (most recent call last):
  File "<console>", line 1, in <module>
hapi.InvalidArgumentError: Invalid argument given: Invalid id.

Can anyone explain what goes in this 'Sop/MyType' part?:
# Assuming we have a loaded an asset which defines a SOP type `MyType`
node_id = hapi.createNode(session, -1, 'Sop/MyType')

Here's my code:

import hapi
options=hapi.ThriftServerOptions() 
process_id = hapi.startThriftSocketServer(options, 9090, log_file="C:\\Users\\m.zaras\\Desktop\\headless_houdini\\log_file.txt")  
session=hapi.createThriftSocketSession('localhost',9090)
cook_options=hapi.CookOptions()
hapi.initialize(session,cook_options)
hda_bytes=open('C:\\Users\\m.zaras\\Desktop\\headless_houdini\\mydigitalasset.hdalc','rb').read()lib_id=hapi.loadAssetLibraryFromMemory(session,hda_bytes,len(hda_bytes),True)

[b]node_id=hapi.createNode(session,-1,'Sop/MyType')[/b]
node_info=hapi.getNodeInfo(session,node_id)



Is using hapi the easiest/only way to work on a HOudini file without the UI/headless?
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mandrake0
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your lib path is wrong python3.7 doesn't exist in Houdini 19.5.
C:\Program Files\Side Effects Software\Houdini 19.5.569\houdini\python3.9libs

when you use hython you can import directly hou, in a python shell you need to import the lib.
hython is just houdini python shell with no UI it's the simplest way but not headless.

i dont have a hapi example but for hython i have a snippet.

Import:
try:
    import hou
except ImportError:
    print 'There is a Problem in the File: server.py please edit the path to houdini installation'
    sys.path.append("C:\\Program Files\\Side Effects Software\\Houdini 19.5.569\\houdini\\python3.9libs")
    import hou

Load a Hip File:
 hip_file = "test.hipnc"
 hou.hipFile.load(hip_file)
after that you can access the nodes like you would be inside Houdini in the Python Shell.

i haven't found a standalone lib or pip command of hapi.py outside the python libs folder but i think if you want to have a headless setup you need only the 3 files (hapi.exp, hapi.lib, hapi.pyd) in the houdini/python3.9libs folder in your custom python project.
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KatanaPoland
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Hi @mandrake0, thanks for your reply.

your lib path is wrong python3.7 doesn't exist in Houdini 19.5.
C:\Program Files\Side Effects Software\Houdini 19.5.569\houdini\python3.9libs
I have Houdini 19.5.569 and I only have python3.7libs in this directory

I followed your example and I get this error when I run it in powershell with: python "path_to_script.py" :

Traceback (most recent call last):
  File "C:\Users\<myusername>\Desktop\script_to_run_in_hython.py", line 8, in <module>
    import hou
  File "C:\Program Files\Side Effects Software\Houdini 19.5.569\houdini\python3.7libs\hou.py", line 28, in <module>
    import _hou
ImportError: DLL load failed while importing _hou: the specified module could not be found.


I ended up running hython.exe instead of powershell since it's got hou already integrated. But I'd love to learn how to manage to install hou with python not on hython.
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mandrake0
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Joined: June 2006
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Sorry i haven't seen that there exist a Python 3.7 Build.

Found a Article about it:
https://www.sidefx.com/docs/houdini/hom/commandline.html [www.sidefx.com]

This should work with a normal Python Runtime.

import os, sys

# import Python Libs and add Path for the Dll Files 
sys.path.append("C:\\Program Files\\Side Effects Software\\Houdini 19.5.569\\houdini\\python3.7libs")
os.add_dll_directory("C:\\Program Files\\Side Effects Software\\Houdini 19.5.569\\bin")

import hou

# Testing, just change the file path 
hou.hipFile.load("c:\\temp\\test.hiplc")
n = hou.node('/obj/box')
# Scale Value is set to 0.123
print(n.parm("scale").eval())

Attachments:
powershell.png (43.2 KB)
test.hiplc (132.1 KB)

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KatanaPoland
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Thanks mandrake0, it worked! Turns out os.add_dll_directory is only available in Python 3.8 and above, so I reinstalled my Houdini from version py 37 to default (with python 3.9), installed python 3.9.1 and entered python shell with py -3.9 to avoid conflicts with Houdini python version.

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