Slicer API


Check out these developer tutorials to get started with customizing and extending 3D Slicer using Python scripting or C++.


Majority of Slicer core modules and all basic infrastructure are implemented in C++. Documentation of these classes are available at:


Doxygen-style documentation

Slicer core infrastructure is mostly implemented in C++ and it is made available in Python in the slicer namespace. Documentation of these classes is available at:

This documentation is generated using the Doxygen tool, which uses C++ syntax. The following rules can help in interpreting this documentation for Python:

  • Qt classes (class name starts with q): for example, qSlicerMarkupsPlaceWidget

  • VTK classes VTK classes (class name starts with vtk): for example, vtkMRMLModelDisplayNode

  • Public Types: most commonly used for specifying enumerated values (indicated by enum type). These values can be accessed as slicer.className.typeName, for example slicer.qSlicerMarkupsPlaceWidget.HidePlaceMultipleMarkupsOption

  • Properties: these are values that are accessible as object attributes in Python and can be read and written as objectName.propertyName. For example:

    >>> w = slicer.qSlicerMarkupsPlaceWidget()
    >>> w.deleteAllMarkupsOptionVisible
    >>> w.deleteAllMarkupsOptionVisible=False
    >>> w.deleteAllMarkupsOptionVisible
  • Public slots: publicly available methods. Note that setSomeProperty methods show up in the documentation but in Python these methods are not available and instead property values can be set using someProperty = ....

  • Signals: signals that can be connected to Python methods

    def someFunction():
    b = qt.QPushButton("MyButton")
    b.connect("clicked()", someFunction)  # someFunction will be called when the button is clicked
  • Public member functions: methods that have Q_INVOKABLE keyword next to them are available from Python. virtual and override specifiers can be ignored.

    • className (for Qt classes): constructor, shows the arguments that can be passed when an object is created
    • New (for VTK classes): constructor, never needs an argument
    • ~className: destructor, can be ignored, Python calls it automatically when needed
    • SafeDownCast (for VTK classes): not needed for Python, as type conversions are automatic
  • Static Public Member Functions: can be accessed as slicer.className.memberFunctionName(arguments) for example: slicer.vtkMRMLModelDisplayNode.GetSliceDisplayModeAsString(0)

  • Protected Slots, Member Functions, Attributes: for internal use only, not accessible in Python

  • Mapping commonly used data types from C++ documentation to Python:

    • void -> Python: if the return value of a method is this type then it means that no value is returned
    • someClass* (object pointer) -> Python: since Python takes care of reference counting, it can be simply interpreted in Python as someClass. The called method can modify the object.
    • int, char, short (with optional signed or unsigned prefix) -> Python: int
    • float, double -> Python: float
    • double[3] -> Python: initialize a variable before the method call as point = np.zeros(3) (or point = [0.0, 0.0, 0.0]) and use it as argument in the function
  • const char *, std::string, QString, const QString& -> Python: str - bool -> Python: bool