how to request a service present in different package

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I am trying to call a service present in package B (Python) from package A (c++).

When i run the code it says unable to find the header file (say packageB/service.h) If i call a service present in Package A then its working fine.

Basically the question is how to request a service present in different package which is implemented in python.

I included the package dependencies in package.xml. Still no result..

Any idea what is wrong ??