No module or function named error in Python custom function with MATLAB

Hi @Poulomi,

I have analyzed your error stack trace, and the persistent ModuleNotFoundError: No module named 'atmos' indicates that my initial approach of correcting the sys.path configuration hasn't resolved the underlying issue. After analyzing your recent error trace:

     Error in <frozen importlib>_find_and_load_unlocked (line 1324)
     Python Error: ModuleNotFoundError: No module named 'atmos'

This specific error signature indicates that Python's import machinery cannot locate the atmos package in its module search path, despite sys.path modifications. This typically occurs when:

1. Package Initialization Failure: Missing or corrupted _init_.py files 2. MATLAB's Python Interpreter State: Cached import failures persisting across attempts 3. File System Permissions: MATLAB's Python subprocess lacking read access 4. Package Structure Malformation: Incorrect directory hierarchy from extraction

So, I will suggest implement a direct module access strategy that bypasses MATLAB's Python package resolution entirely. Execute the following steps in sequence:

Step 1: MATLAB-Python Environment Reset

% Force clear Python interpreter state
clear classes
py.importlib.invalidate_caches();

Step 2: Direct Module Path Configuration

% Target the specific directory containing moisture.py
moistureModulePath = 'C:\pganguli\Pyscripts\atmos-main\atmos-    main\atmos\';
if count(py.sys.path, moistureModulePath) == 0
  insert(py.sys.path, int64(0), moistureModulePath);
end

% Diagnostic verification

fprintf('Python path[0]: %s\n', string(py.sys.path{1}));

Step 3: Standalone Module Import

% Import moisture.py as independent module (not package 
submodule)
try
  py.importlib.import_module('moisture');
  fprintf('SUCCESS: moisture module imported\n');
catch ME
  fprintf('FAILED: %s\n', ME.message);
  return;
end

Step 4: Function Access Verification

% Direct function call bypassing package hierarchy
try
  q =   py.moisture.specific_humidity_from_dewpoint_temperature(P,T);
  fprintf('SUCCESS: Function executed, result type: %s\n',     class(q));
catch ME
  fprintf('FAILED: %s\n', ME.message);
end

Step 5: Module Introspection

% Verify available functions
available_functions = py.dir(py.moisture);
fprintf('Available functions in moisture module:\n');
for i = 1:length(available_functions)
  if ~startsWith(string(available_functions{i}), '__')
      fprintf('  - %s\n', string(available_functions{i}));
  end
end

So, this time by importing moisture.py directly as a top-level module rather than accessing it through the atmos.moisture package path, you circumvent:

• Python's package discovery protocol
• Hierarchical import resolution
• Package initialization dependencies

Please Report Back: Execute each step and provide: 1. Console output from Steps 2-3 (including any error messages) 2. The specific error message if Step 3 fails 3. Results from Step 5 (function listing)

Try this systematic approach and provide precise diagnostic information for further troubleshooting.

Let me know how it goes!

Hi @Poulomi,

Thank you for sharing your detailed outputs. I’ve carefully reviewed each of the errors you encountered and want to provide a systematic explanation and resolution. The goal is to ensure MATLAB can call your Python functions seamlessly without further trial-and-error.

1. Brace Indexing Error

Error:

Brace indexing into the result of a function call is not supported.

Root Cause: MATLAB does not allow `{}` indexing directly on the return value of a function. `py.sys.path` returns a Python list object, which must first be assigned to a MATLAB variable.

V = py.sys.path; % assign first disp(V{1}); % then access

2. ModuleNotFoundError: No module named 'atmos'

Error:

FAILED: Python Error: No module named 'atmos'

Root Cause: You added the `atmos` folder itself to `sys.path`. Python expects the *parent directory of the package* in `sys.path`, and modules must be imported using the *full package hierarchy*.

Solution:

parentPath = 'C:\pganguli\Pyscripts\atmos_main\'; % parent folder of 'atmos' if count(py.sys.path, parentPath) == 0 insert(py.sys.path, int64(0), parentPath); end

py.importlib.import_module('atmos.moisture'); % import using full package path

3. Unable to resolve py.moisture.function

Error:

FAILED: Unable to resolve the name 'py.moisture.specific_humidity_from_dewpoint_temperature'

Root Cause: `moisture.py` is a submodule of `atmos`. MATLAB cannot access it directly as `py.moisture`. Python requires functions to be called as `package.module.function`.

Solution:

q = py.atmos.moisture.specific_humidity_from_dewpoint_temperature(P, T);

4. Attempted full path import fails

Error:

py.importlib.import_module("C:\pganguli\Pyscripts\atmos_main\atmos\atmos.moisture.py")

Root Cause: `import_module` only accepts *module/package names*, not absolute paths. Python interprets the string literally and cannot find a module with that name.

Solution: Always import using the package name relative to `sys.path`:

py.importlib.import_module('atmos.moisture');

5. Environment Reset and Diagnostics

To avoid cached import issues:

clear classes py.importlib.invalidate_caches();

Verify that MATLAB sees the path:

V = py.sys.path; disp(V);

List available functions inside `moisture`:

available_functions = py.dir(py.atmos.moisture); disp(available_functions);

Root Cause Summary

1. `sys.path` pointed to the package folder, not its parent. 2. Direct calls like `py.moisture` bypass Python’s package hierarchy. 3. Absolute path imports are invalid in Python. 4. MATLAB caches imports; clearing classes and invalidating caches is required.

Following these guidelines precisely will resolve the errors and enable seamless MATLAB-Python integration.