Coming from C

Compared to the C interface for ITAPS, PyTAPS has some important differences designed to take advantage of Python language features. Users familiar with the C interface should review the changes below.


To reduce the number of methods that must be memorized when using these interfaces, PyTAPS coalesces all entity, entity array, and entity set functions into a single function where appropriate. For instance, the iMesh functions iMesh_addEntToSet, iMesh_addEntArrToSet, and iMesh_addEntSet are all called by itaps.iMesh.EntitySet.add(). Which C API function is ultimately called is determined by the type of the argument passed to add.

One notable exception to this rule is itaps.iMesh.Mesh.createEnt() and itaps.iMesh.Mesh.createEntArr(), which have the same signatures and so cannot be overloaded based on the types of the arguments.

Return Values

Instead of relying on out-values to return data from interface functions, PyTAPS uses the simpler method of merely returning the data. In cases where multiple return values are needed, PyTAPS returns a tuple of the values (or a namedtuple in Python 2.6+). As a notable exception to this, return values that contain offset arrays are wrapped into helper classes, located in itaps.helpers.

Error Handling

All instances of the out-value int *err in functions have been replaced with Python ITAPSErrors that are raised if an error of some kind occurs.


In the C interface, arrays are passed as pairs of parameters when used as input (type *data, int size) and as triples of parameters when used as output (type **data, int *alloc, int *size). The PyTAPS interface uses Numpy for all array data, and so the size is passed implicitly along with the array. Since Python programs (generally) do not manually manage their own memory, the alloc parameter is similarly eliminated.

Storage Order

By default, PyTAPS uses interleaved storage – that is, coordinates are arranged as ((x1, y1, z1), (x2, y2, z2), ...) – regardless of the default storage order in the underlying ITAPS interface. This is done to allow more idiomatic use of arrays of coordinates in Python.

The out Argument

Most functions that return arrays also accept an optional argument named out. Supply this argument if you’d like to use the memory buffer of another array to hold the result of the function call.

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