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IMP Manual  develop.5a6c335,2019/01/20
Coding conventions

To ensure code consistency and readability, certain conventions must be adhered to when writing code for IMP. Some of these conventions are automatically checked for by source control before allowing a new commit, and can also be checked yourself in new code by running

All new code should also conform to the previously-described naming and interface conventions.


All C++ headers and code should be indented with 2-space indents. Do not use tabs. can help you do this formatting automatically.

All Python code should conform to the Python style guide. In essence this translates to 4-space indents, no tabs, and similar class, method and variable naming to the C++ code. You can ensure that your Python code is correctly indented by using the script.


In addition to the previously-described naming and interface conventions, developers should be aware that

  • all preprocessor symbols must begin with IMP.
  • names of files that implement a single class should be named for that class; for example the SpecialVector class could be implemented in SpecialVector.h and SpecialVector.cpp
  • files that provide free functions or macros should be given names separated_by_underscores, for example container_macros.h
  • command line tools should also be given names separated_by_underscores and should not have a file extension (such as .py). (Note also that since tools are installed, care should be taken to give them non-generic names so they don't conflict with other programs users may have installed on their system. Also consider using IMP::CommandDispatcher to provide a single command line interface to many individual Python scripts, rather than making each one a command line tool.)
  • Functions which take a parameter which has units should have the unit as part of the function name, for example IMP::atom::SimulationParameters::set_maximum_time_step_in_femtoseconds(). Remember the Mars orbiter. The exception to this is distance and force numbers which should always be in angstroms and kcal/mol/angstrom respectively unless otherwise stated.

Passing and storing data

  • When a class or function takes a set of particles which are expected to be those of a particular type of decorator, it should take a list of decorators instead. eg IMP::core::transform() takes a IMP::core::XYZ. This makes it clearer what attributes the particle is required to have as well as allows functions to be overloaded (so there can be an IMP::core::transform() which takes IMP::core::RigidBody particles instead).
  • IMP::Restraint and IMP::ScoreState classes should generally use a IMP::SingletonContainer (or other type of Container) to store the set of IMP::Particle objects that they act on. Alternatively, take and store one or more IMP::ParticleIndex objects (or related types, such as IMP::ParticleIndexPair).
  • Store collections of IMP::Object-derived objects of type Name using a Names. Declare functions that accept them to take a NamesTemp (Names is a NamesTemp). Names are reference counted (see IMP::Object for details); NamesTemp are not. Store collections of particles using IMP::ParticleIndexes, rather than using IMP::Particles or decorators.
  • To handle floating-point data, use the standard C++ double type. (In most cases on modern 64-bit systems, float isn't any more efficient.) Use the IMP::Float type (and derived types, such as IMP::FloatPair) only to work with floating-point attributes of IMP::Model objects. (Similarly, use int and std::string for integer and string data, except for accessing IMP::Model attributes where the IMP::Int and IMP::String types should be utilized.)
  • To work with vectors of data, use IMP::Vector. It performs similarly to std::vector but adds extra functionality, and turns on bounds checks when IMP is built in debug mode.


All values must have a show method which takes an optional std::ostream and prints information about the object (see IMP::Array::show() for an example). Add a write method if you want to provide output that can be read back in.


Classes and methods should use IMP exceptions to report errors. See IMP::Exception for a list of existing exceptions (click on the "Inheritance diagram" link on that page). See checks for more information.



Each module has an internal namespace, eg IMP::atom::internal, and an internal include directory IMP/atom/internal. Any function which is

  • not intended to be part of the API,
  • not documented,
  • liable to change without notice,
  • or not tested

should be declared in an internal header and placed in the internal namespace.

The functionality in such internal headers is

  • not exported to Python
  • and not part of the documented API

As a result, such functions do not need to obey all the coding conventions (but we recommend that they do).

C++ 11

IMP now turns on C++ 11 support when it can. However, since compilers are still quite variable in which C++ 11 features they support, it is not advisable to use them directly in IMP code at this point. To aid in their use when practical we provide several helper macros:

  • IMP_OVERRIDE inserts the override keyword when available
  • IMP_FINAL inserts the final keyword when available

More will come.