Refine find_nexus_module search locations and error handling by ye-luo · Pull Request #5767 · QMCPACK/qmcpack

ye-luo · 2026-01-28T22:09:12Z

Proposed changes

Currently, nexus executables require a closely coupled nexus modules, namely

<nexus_root>/bin # contains nexus exectuables
<nexus_root>/nexus #contains nexus module files

find_nexus_module honors this layout and verifies nexus module import.
qmca has the gold implementation and other scripts follow.

I also corrected the following discovery path.

nexus_lib = os.path.realpath(os.path.join(__file__,'..','..','..','nexus'))

nexus internal lookup should not go beyond <nexus_root>. Simply use

nexus_lib = os.path.realpath(os.path.join(__file__,'..','..'))

What type(s) of changes does this code introduce?

Refactoring (no functional changes, no api changes)
Other (please describe): more error traps

Does this introduce a breaking change?

No

What systems has this change been tested on?

laptop

Checklist

- I have read the pull request guidance and develop docs
- This PR is up to date with the current state of 'develop'
- Code added or changed in the PR has been clang-formatted
- This PR adds tests to cover any new code, or to catch a bug that is being fixed
- Documentation has been added (if appropriate)

ye-luo · 2026-01-28T22:09:24Z

Test this please

brockdyer03

As best I can tell, while this code does unify the find_nexus_modules function, it doesn't do anything to stop enforcement of the location of the executables being with the rest of Nexus. Perhaps a separate bit of code that checks if you're in a QMCPACK install directory would fix it?

nexus/bin/nexus_modules.py

brockdyer03 · 2026-01-28T23:31:23Z

nexus/bin/nexus_modules.py

+    nexus_lib2 = os.path.realpath(os.path.join(nexus.__file__,'..','..'))
+
+    # ensure closely coupled nexus module is in use.
+    if nexus_lib != nexus_lib2:


This is the line that is probably going to continue failing if the executables get moved. The enforcement of location of the current file with the location of Nexus means that this will likely still result in a failure if the executables are moved.

Unfortunately that is a current requirement.

We should keep the strict association in this PR. We can remove it in a following PR once a decision is made.

ye-luo · 2026-01-29T00:51:12Z

The introduced nexus_modules.py generate __pycache__ and prevents executing nexus/install.

qmcpack/nexus/install

Line 116 in 01c9846

execute('cp {0}/bin/* {1}'.format(source_dir,install_dir))

err: b"cp: -r not specified; omitting directory '/home/yeluo/opt/qmcpack/nexus/bin/__pycache__'\n"

brockdyer03 · 2026-01-29T01:22:02Z

To be honest I forgot about __pycache__. That gets created whenever you import Python modules that are not your current module. Usually that only gets made in qmcpack/nexus/nexus, but since there was a .py file added to qmcpack/nexus/bin it'll make one if you run anything before doing the copy. I don't think that creating a separate .py file is a viable option.

I think since @jtkrogel said he was fine with most of the executables not actually enforcing association with the rest of Nexus (except for nxs-test) it would probably be fine to just delete find_nexus_modules from all of the files (again, except for nxs-test) and put the onus on the user to ensure their Python path is set properly.

…y nexus exectuables.

ye-luo · 2026-01-29T04:35:34Z

To be honest I forgot about __pycache__. That gets created whenever you import Python modules that are not your current module. Usually that only gets made in qmcpack/nexus/nexus, but since there was a .py file added to qmcpack/nexus/bin it'll make one if you run anything before doing the copy.

You analysis is correct

I don't think that creating a separate .py file is a viable option.

simply avoid files starting with underscore. taken care by #5768

I think since @jtkrogel said he was fine with most of the executables not actually enforcing association with the rest of Nexus (except for nxs-test) it would probably be fine to just delete find_nexus_modules from all of the files (again, except for nxs-test) and put the onus on the user to ensure their Python path is set properly.

I actually prefer all the nexus executable runnable without setting PYTHONPATH by the user or by a virtual environment. They must be exactly matched to the nexus module in the same git commit. The current strict coupling requirement made nexus executables invulnerable to hidden PYTHONPATH changes.

jtkrogel · 2026-01-29T10:41:15Z

Need to catch up with the discussion here. From what I understand of our prior discussion, no decisions had been made about enforcing strict association between the binaries and nexus modules (though I favor retaining it).

jtkrogel · 2026-01-29T10:50:02Z

On a closer look, I really don't see the virtue of including a non-binary (find_nexus_modules.py) in the binaries directory. I can understand the desire to remove all instances of code duplication, but I think the unwieldiness of this change is worse.

brockdyer03 · 2026-01-29T11:08:14Z

simply avoid files starting with underscore. taken care by #5768

I think this could potentially introduce unwanted side effects. For example, qmcpack/nexus/nexus has a file __init__.py which was renamed from nexus.py to be compliant with packaging guidelines. Without that file, the entire package will stop working, so if that copy script ever gets duplicated it will cause significant errors that will be hard to trace.

prckent

nexus/bin is for directly shell executable programs; putting a not directly callable function there is non-standard and will confuse users (etc.). Could it be made a verify_nexus_installation utility that can also be called directly? If this route works, we could expand it subsequently to include a reporting of the various nexus required and optional package imports.

…in nxs-test

ye-luo · 2026-01-29T18:55:14Z

@prckent verify_nexus_installation has been introduced. I couldn't find a clean way to avoid code duplication. Using sub-process to invoke verify_nexus_installation is still very messy. So just copied find_nexus_module into each script noting that the reference copy is from verify_nexus_installation

jtkrogel · 2026-02-02T17:27:24Z

It is the job of nxs-test to validate the installation, so having verify_nexus_installation is redundant and misleading (it verifies nothing but paths while the installation could still be broken). The "gold" implementation of the path checking should reside in nxs-test.

jtkrogel · 2026-01-29T10:43:18Z

nexus/bin/nexus_modules.py

+    nexus_lib2 = os.path.realpath(os.path.join(nexus.__file__,'..','..'))
+
+    # ensure closely coupled nexus module is in use.
+    if nexus_lib != nexus_lib2:


We should keep the strict association in this PR. We can remove it in a following PR once a decision is made.

jtkrogel · 2026-01-29T10:44:22Z

nexus/bin/nxs-test

    from time import time # used to get user wall clock rather than cpu time
    tstart_all = time()

-    testing_wrong_nexus_install = False


Why is this deleted?

Please reply. This should not be removed.

The replaced find_nexus_module did the work already.

Due to the current requirement of nxs-test that exception should not be raise by itself. The gold implementation can not be used and kept by nxs-test. I reverted most of the changes in nxs-test.

jtkrogel · 2026-02-02T17:29:03Z

nexus/bin/verify_nexus_installation

@@ -0,0 +1,38 @@
+#! /usr/bin/env python3


Should be removed. See comment in the conversation/chat.

ye-luo · 2026-02-02T20:49:22Z

It is the job of nxs-test to validate the installation, so having verify_nexus_installation is redundant and misleading (it verifies nothing but paths while the installation could still be broken). The "gold" implementation of the path checking should reside in nxs-test.

Currently nxs-test needs extra work to have a proper installation. Consider the added tool a stopgap utility.

…executables

ye-luo · 2026-02-03T22:33:48Z

@prckent I removed verify_nexus_Installation that @jtkrogel considered redundant and we had a hard time to agree on what exactly it should serve and where it should be hosted. The same check exists in every nexus binary should be sufficient to catch the issue and inform users.

jtkrogel · 2026-02-04T15:05:59Z

The implementation of find_nexus_modules displays error messages unclear to the user. It also masks import errors internal to Nexus modules which misleads users.

Here is an updated version that solves these problems:

def find_nexus_modules():
    import os
    import sys
    # Prepend the assumed path of a folder containing the closely coupled nexus module to module search path
    # It points to the top Nexus directory not necessarily the top QMCPACK directory.
    nexus_lib = os.path.realpath(os.path.join(__file__,'..','..'))

    # "import nexus" will fail due to missing module files if nexus/__init__.py does not exists
    nexus_init = os.path.join(nexus_lib,'nexus','__init__.py')
    if not os.path.exists(nexus_init):
        print('\nNexus modules are required but cannot be imported!'
              '\nMake sure Nexus modules are available at:'
              '\n  '+nexus_lib+'\n')
        sys.exit(1)

    # check import of nexus modules
    sys.path.insert(0,nexus_lib)
    try:
        import nexus
    except Exception as err:
        print('\nImporting Nexus modules failed for an unknown reason.'
              '\nThis is likely a developer error.'
              '\nFor more information, the original exception is reproduced below.'
              '\nPlease report this error to the Nexus developers.'+2*'\n')
        import traceback
        exc_type, exc_value, exc_traceback = sys.exc_info()
        exc_lines = traceback.format_exception(exc_type, exc_value, exc_traceback)
        for line in exc_lines:
            print(line.rstrip())
        print()
        sys.exit(1)

    # ensure closely coupled nexus module is in use.
    nexus_lib2 = os.path.realpath(os.path.join(nexus.__file__,'..','..'))
    if nexus_lib != nexus_lib2:
        exe = sys.argv[0].split('/')[-1]
        exe_full_path = os.path.abspath(exe)
        print('\nBroken Nexus installation!' 
              +'\n  {} is required to reside in the Nexus module directory.'.format(exe)
              +'\n  {} location      {}   : {}'.format(exe,' '*max(0,8-len(exe)),exe_full_path)
              +'\n  Nexus module directory    : ' + nexus_lib2+'\n')
        sys.exit(1)
#end def find_nexus_modules

jtkrogel · 2026-02-04T15:08:13Z

Here is a comparison of the error messages the user will see based on the original and updated find_nexus_modules above:

Nexus modules aren't located where qmca needs them

Original:

>./qmca 
Traceback (most recent call last):
  File "/home/j1k/repositories/nexus_dev_as_package/nexus/bin/./qmca", line 18, in find_nexus_modules
    import nexus
ModuleNotFoundError: No module named 'nexus'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/j1k/repositories/nexus_dev_as_package/nexus/bin/./qmca", line 36, in <module>
    find_nexus_modules()
  File "/home/j1k/repositories/nexus_dev_as_package/nexus/bin/./qmca", line 20, in find_nexus_modules
    raise ImportError(
ImportError: Nexus module is required but cannot be imported! Make sure Nexus module available under /home/j1k/repositories/nexus_dev_as_package/nexus

Updated:

>./qmca 

Nexus modules are required but cannot be imported!
Make sure Nexus modules are available at:
  /home/j1k/repositories/nexus_dev_as_package/nexus

jtkrogel · 2026-02-04T15:09:40Z

Nexus modules have a bad import internally

Original:

>./qmca
Traceback (most recent call last):
  File "/home/j1k/repositories/nexus_dev_as_package/nexus/bin/./qmca", line 26, in find_nexus_modules
    import nexus
  File "/home/j1k/repositories/nexus_dev_as_package/nexus/nexus/__init__.py", line 43, in <module>
    from .pwscf   import Pwscf  , PwscfInput  , PwscfAnalyzer  , generate_pwscf_input  , generate_pwscf
  File "/home/j1k/repositories/nexus_dev_as_package/nexus/nexus/pwscf.py", line 29, in <module>
    import bad_module
ModuleNotFoundError: No module named 'bad_module'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/j1k/repositories/nexus_dev_as_package/nexus/bin/./qmca", line 44, in <module>
    find_nexus_modules()
  File "/home/j1k/repositories/nexus_dev_as_package/nexus/bin/./qmca", line 28, in find_nexus_modules
    raise ImportError(
ImportError: Nexus module is required but cannot be imported! Make sure Nexus module available under /home/j1k/repositories/nexus_dev_as_package/nexus

Updated:

>./qmca

Importing Nexus modules failed for an unknown reason.
This is likely a developer error.
For more information, the original exception is reproduced below.
Please report this error to the Nexus developers.


Traceback (most recent call last):
  File "/home/j1k/repositories/nexus_dev_as_package/nexus/bin/./qmca", line 26, in find_nexus_modules
    import nexus
  File "/home/j1k/repositories/nexus_dev_as_package/nexus/nexus/__init__.py", line 43, in <module>
    from .pwscf   import Pwscf  , PwscfInput  , PwscfAnalyzer  , generate_pwscf_input  , generate_pwscf
  File "/home/j1k/repositories/nexus_dev_as_package/nexus/nexus/pwscf.py", line 29, in <module>
    import bad_module
ModuleNotFoundError: No module named 'bad_module'

jtkrogel · 2026-02-04T15:10:51Z

Nexus modules execute bad code during import:

Original:

>./qmca
Traceback (most recent call last):
  File "/home/j1k/repositories/nexus_dev_as_package/nexus/bin/./qmca", line 44, in <module>
    find_nexus_modules()
  File "/home/j1k/repositories/nexus_dev_as_package/nexus/bin/./qmca", line 26, in find_nexus_modules
    import nexus
  File "/home/j1k/repositories/nexus_dev_as_package/nexus/nexus/__init__.py", line 43, in <module>
    from .pwscf   import Pwscf  , PwscfInput  , PwscfAnalyzer  , generate_pwscf_input  , generate_pwscf
  File "/home/j1k/repositories/nexus_dev_as_package/nexus/nexus/pwscf.py", line 30, in <module>
    bad_int = int('6.66')
ValueError: invalid literal for int() with base 10: '6.66'

Updated:

>./qmca

Importing Nexus modules failed for an unknown reason.
This is likely a developer error.
For more information, the original exception is reproduced below.
Please report this error to the Nexus developers.


Traceback (most recent call last):
  File "/home/j1k/repositories/nexus_dev_as_package/nexus/bin/./qmca", line 26, in find_nexus_modules
    import nexus
  File "/home/j1k/repositories/nexus_dev_as_package/nexus/nexus/__init__.py", line 43, in <module>
    from .pwscf   import Pwscf  , PwscfInput  , PwscfAnalyzer  , generate_pwscf_input  , generate_pwscf
  File "/home/j1k/repositories/nexus_dev_as_package/nexus/nexus/pwscf.py", line 30, in <module>
    bad_int = int('6.66')
ValueError: invalid literal for int() with base 10: '6.66'

jtkrogel · 2026-02-04T15:11:52Z

Broken install

Original:

>./qmca
Traceback (most recent call last):
  File "/home/j1k/repositories/nexus_dev_as_package/nexus/bin/./qmca", line 60, in <module>
    find_nexus_modules()
  File "/home/j1k/repositories/nexus_dev_as_package/nexus/bin/./qmca", line 44, in find_nexus_modules
    raise Exception('Broken Nexus installation! Nexus Python scripts are required to reside in the directory that contains the Nexus module.'
Exception: Broken Nexus installation! Nexus Python scripts are required to reside in the directory that contains the Nexus module.
Nexus Python script         : /home/j1k/repositories/nexus_dev_as_package/nexus/bin/qmca
Nexus module root directory : /home/j1k/repositories/nexus_dev_as_package/nexus

Updated:

>./qmca

Broken Nexus installation!
  qmca is required to reside in the Nexus module directory.
  qmca location             : /home/j1k/repositories/nexus_dev_as_package/nexus/bin/qmca
  Nexus module directory    : /home/j1k/repositories/nexus_dev_as_package/nexus

jtkrogel · 2026-02-04T15:14:12Z

Above are comparisons of original and updated code for find_nexus_modules for these failure cases:

Nexus modules aren't located where qmca needs them
Nexus modules have a bad import internally
Nexus modules execute bad code during import
Broken install

The error messages are more concise and tell the user what to do.

With minor modifications, this version might be sufficient for nxs-test.

jtkrogel

Looks solid now.

ye-luo · 2026-02-05T16:13:11Z

@prckent ping

prckent · 2026-02-05T16:24:22Z

I will test this "by hand".

prckent

In my testing, running qmca directly without any PATH or PYTHONPATH set works correctly, as does using a link to qmca. Copying qmca elsewhere and using it correctly gives an error. This clearly a nice improvement. However, I think we can use this opportunity to further improve the error messages for users:

qmcuser@9abc81ade268:~/test_simple_H2O$ $HOME/qmcpack/nexus/bin/qmca -q ev -e 200 --sac LiH.s002.dmc.dat 
                            LocalEnergy               Variance           ratio 
LiH  series 2  -8.541570 +/- 0.005672   16.4   0.142099 +/- 0.002624    6.3   0.0166 
qmcuser@9abc81ade268:~/test_simple_H2O$ echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/opt/qe/bin
qmcuser@9abc81ade268:~/test_simple_H2O$ echo $PYTHONPATH
/opt/pyscf:/home/qmcuser/qmcpack/src/QMCTools
qmcuser@9abc81ade268:~/test_simple_H2O$ ln -s $HOME/qmcpack/nexus/bin/qmca  .
qmcuser@9abc81ade268:~/test_simple_H2O$ ./qmca -q ev -e 200 --sac LiH.s002.dmc.dat  
                            LocalEnergy               Variance           ratio 
LiH  series 2  -8.541570 +/- 0.005672   16.4   0.142099 +/- 0.002624    6.3   0.0166 
qmcuser@9abc81ade268:~/test_simple_H2O$ rm -f qmca 
qmcuser@9abc81ade268:~/test_simple_H2O$ cp ~/qmcpack/nexus/bin/qmca .
qmcuser@9abc81ade268:~/test_simple_H2O$ ./qmca -q ev -e 200 --sac LiH.s002.dmc.dat

File /home/qmcuser/nexus/__init__.py does not exist!
Broken Nexus installation!
Make sure Nexus modules are available at:
  /home/qmcuser

I suggest the error be expanded to something like the following. We can not expect users to be familiar with file layout in modules, so providing more info should help.

Expected file /home/qmcuser/nexus/__init__.py does not exist!
Broken Nexus installation! All expected files not found.
Make sure Nexus modules are available at:
  /home/qmcuser
Expecting to find files including
/home/qmcuser/nexus/__init__.py
/home/qmcuser/nexus/basis.py

ye-luo · 2026-02-05T19:53:03Z

@prckent I agree that we can not expect users to be familiar with file layout in modules.
For that reason, "Broken Nexus installation!" is a strong message to users and they should check Nexus manual about installation. I will emphasize this in the printout.

Expecting to find files including
/home/qmcuser/nexus/__init__.py
/home/qmcuser/nexus/basis.py

can potentially encourage users copying two mentioned files. It won't work well.

How about the following?

Expected file /home/qmcuser/nexus/__init__.py does not exist!
Broken Nexus installation! Please follow Nexus manual regarding installation.

The first line must be kept reflecting the exact failed check and also indicating a correct installation should provide that file.

prckent · 2026-02-05T19:57:30Z

Good improvement. https://nexus-workflows.readthedocs.io/en/latest/installation.html seems sufficiently up to date. Could be expanded e.g. when the installer gets updated.

…executables

ye-luo · 2026-02-05T20:29:55Z

@prckent updated.

prckent

Thanks Ye and all.

prckent · 2026-02-05T20:32:14Z

Test this please

brockdyer03 · 2026-02-05T23:23:17Z

Good improvement. https://nexus-workflows.readthedocs.io/en/latest/installation.html seems sufficiently up to date. Could be expanded e.g. when the installer gets updated.

That part of the manual will be almost completely rewritten when the packaging PR (#5742) gets merged, all in reStructuredText. I'd advise waiting for a rewrite until after that PR is merged if at all possible.

brockdyer03 reviewed Jan 28, 2026

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ye-luo marked this pull request as draft January 29, 2026 00:45

ye-luo force-pushed the consolidate-nexus-executables branch 2 times, most recently from 149eedb to 5d9f62e Compare January 29, 2026 01:18

Introduce nexus_modules to handle consistent nexus module searching b…

0441e82

…y nexus exectuables.

ye-luo force-pushed the consolidate-nexus-executables branch from 5d9f62e to 0441e82 Compare January 29, 2026 04:17

ye-luo marked this pull request as ready for review January 29, 2026 04:41

prckent requested changes Jan 29, 2026

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Keep find_nexus_module within each Nexus script. Gold implementation …

bd9bd9f

…in nxs-test

ye-luo changed the title ~~Introduce nexus_modules to handle consistent nexus module searching by nexus exectuables~~ Refine find_nexus_module search locations and error handling Jan 29, 2026

ye-luo force-pushed the consolidate-nexus-executables branch from 4657b08 to 139fac4 Compare January 29, 2026 18:51

ye-luo force-pushed the consolidate-nexus-executables branch from 139fac4 to 5eec27e Compare January 29, 2026 18:55

Introduce verify_nexus_installation

646ad70

ye-luo force-pushed the consolidate-nexus-executables branch from 5eec27e to 646ad70 Compare January 29, 2026 19:01

ye-luo added this to the v4.2.0 Release milestone Jan 29, 2026

jtkrogel requested changes Feb 2, 2026

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ye-luo added 3 commits February 3, 2026 15:44

Merge remote-tracking branch 'origin/develop' into consolidate-nexus-…

27ea395

…executables

Revert changes in nxs-test

4ada190

Remove verify_nexus_installation

c5f7527

Refine based on review.

0df99b5

ye-luo force-pushed the consolidate-nexus-executables branch from b13e284 to 0df99b5 Compare February 4, 2026 19:32

Refine printout

437e5cc

jtkrogel previously approved these changes Feb 4, 2026

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prckent requested changes Feb 5, 2026

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ye-luo added 2 commits February 5, 2026 14:16

Brief concise message.

2c45257

Merge remote-tracking branch 'origin/develop' into consolidate-nexus-…

f509870

…executables

ye-luo dismissed jtkrogel’s stale review via f509870 February 5, 2026 20:29

prckent approved these changes Feb 5, 2026

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prckent merged commit 7b6468e into QMCPACK:develop Feb 6, 2026
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