When working with PythonOCC, you may come across the need to access step instance ids. In this article, we will explore three different ways to solve this problem.

Option 1: Using the OCC API

The first option is to utilize the PythonOCC API to access step instance ids. Here’s how you can do it:

import OCC.Core.STEPControl as STEPControl

# Load the STEP file
step_reader = STEPControl.STEPControl_Reader()
step_reader.ReadFile("path/to/your/step/file.step")

# Transfer the data from the reader to the transfer entity
step_reader.TransferRoots()

# Get the number of roots
num_roots = step_reader.NbRootsForTransfer()

# Iterate over the roots and access the instance ids
for i in range(1, num_roots + 1):
    root = step_reader.RootForTransfer(i)
    instance_id = root.InstanceId()
    print(f"Instance ID for root {i}: {instance_id}")

This code snippet uses the STEPControl_Reader class from the OCC module to read the STEP file. It then transfers the data to the transfer entity and retrieves the number of roots. Finally, it iterates over the roots and accesses the instance ids using the InstanceId() method.

Option 2: Using the STEPImporter class

Another way to access step instance ids is by using the STEPImporter class provided by PythonOCC. Here’s an example:

from OCC.Extend.DataExchange import read_step_file

# Load the STEP file
step_data = read_step_file("path/to/your/step/file.step")

# Access the instance ids
for shape in step_data:
    instance_id = shape.InstanceId()
    print(f"Instance ID: {instance_id}")

In this code snippet, we use the read_step_file function from the OCC.Extend.DataExchange module to load the STEP file. We then iterate over the shapes in the step_data and access the instance ids using the InstanceId() method.

Option 3: Using the STEPControl_Reader class with TopoDS_Shape

The third option involves using the STEPControl_Reader class along with the TopoDS_Shape class from the OCC module. Here’s how you can do it:

import OCC.Core.STEPControl as STEPControl
from OCC.Core.TopoDS import TopoDS_Shape

# Load the STEP file
step_reader = STEPControl.STEPControl_Reader()
step_reader.ReadFile("path/to/your/step/file.step")

# Transfer the data from the reader to the transfer entity
step_reader.TransferRoots()

# Get the number of roots
num_roots = step_reader.NbRootsForTransfer()

# Iterate over the roots and access the instance ids
for i in range(1, num_roots + 1):
    root = step_reader.RootForTransfer(i)
    shape = root.GetObject()
    instance_id = TopoDS_Shape(shape).InstanceId()
    print(f"Instance ID for root {i}: {instance_id}")

In this code snippet, we follow a similar approach as in option 1, but instead of directly accessing the instance ids from the root, we convert the root to a TopoDS_Shape object and then access the instance ids using the InstanceId() method.

After exploring these three options, it is clear that option 1, which utilizes the OCC API, is the better choice. It provides a more direct and efficient way to access step instance ids. However, depending on your specific requirements and the complexity of your project, options 2 and 3 may also be viable alternatives.