# Variant

VTKExamples/Python/Utilities/Variant

### Code

Variant.py

    from __future__ import print_function
    import vtk
    import sys

    # Unicode string for demonstration (etre with circumflex)
    if sys.hexversion >= 0x03000000:
        unicodeEtre = '\xeatre' # unicode in Python 3
    else:
        unicodeEtre = unicode('\xeatre', 'latin1')

    #
    # Basic vtkVariant usage
    #

    # Default constructor
    v = vtk.vtkVariant()
    print("Invalid variant: %r, '%s'" % (v, v.GetTypeAsString()))

    # Copy constructor
    v = vtk.vtkVariant(vtk.vtkVariant("variant"))
    print("Copied variant: %r, '%s'" % (v, v.GetTypeAsString()))

    # Conversion constructors
    v = vtk.vtkVariant(1)
    print("Integer variant: %r, '%s'" % (v, v.GetTypeAsString()))
    v = vtk.vtkVariant(1.0)
    print("Float variant: %r, '%s'" % (v, v.GetTypeAsString()))
    v = vtk.vtkVariant("hello")
    print("String variant: %r, '%s'" % (v, v.GetTypeAsString()))
    v = vtk.vtkVariant(unicodeEtre)
    print("Unicode variant: %r, '%s'" % (v, v.GetTypeAsString()))
    v = vtk.vtkVariant(vtk.vtkStringArray())
    print("Object variant: %r, '%s'" % (v, v.GetTypeAsString()))

    # Explicit type constructor
    v1 = vtk.vtkVariant(1, vtk.VTK_UNSIGNED_SHORT)
    v2 = vtk.vtkVariant(2, v1.GetType())
    print("UShort variant: %r, '%s'" % (v2, v2.GetTypeAsString()))

    # Type checking
    if v2.IsUnsignedShort():
        print("v2 is UnsignedShort")
    else:
        print("v2 is not UnsignedShort, it is", v2.GetTypeAsString())

    # Explicit value extraction
    s = v2.ToString()
    print("String value: %s, %s" % (s, type(s)))
    i = v2.ToInt()
    print("Int value: %i, %s" % (i, type(i)))

    # Automatic argument conversion
    a = vtk.vtkVariantArray()
    a.InsertNextValue(vtk.vtkVariant())
    a.InsertNextValue(1)
    a.InsertNextValue(2.0)
    a.InsertNextValue("hello")
    a.InsertNextValue(unicodeEtre)
    a.InsertNextValue(vtk.vtkVariantArray())
    print("Variant array:")
    for i in range(a.GetNumberOfValues()):
        v = a.GetValue(i)
        print("%i: %r, '%s'" % (i, v, v.GetTypeAsString()))

    # Comparison
    if v2 == vtk.vtkVariant(2):
       print("v2 is equal to 2")
    if v2 > vtk.vtkVariant(1):
       print("v2 is greater than 1")
    if v2 < vtk.vtkVariant(3):
       print("v2 is less than 3")
    if v2 == vtk.vtkVariant("2"):
       print("v2 is equal to '2'")

    # Use as a dict key (hashed as a string)
    d = {}
    d[vtk.vtkVariant(1)] = 0
    d[vtk.vtkVariant('1')] = 1
    d[vtk.vtkVariant()] = 3
    print("Index is %i" % d[vtk.vtkVariant(1.0)])

    #
    # Extra functionality from vtk.util.vtkVariant
    #
    # These are templated functions in C++, but in Python
    # they take the template arg as a string instead,
    # e.g. vtkVariantCreate<unsigned int>(1) becomes
    #      vtkVariantCreate(1, 'unsigned int')

    # Creation
    v = vtk.vtkVariantCreate(1, 'unsigned int')

    # Value extraction
    v = vtk.vtkVariant(6.0)
    f = vtk.vtkVariantExtract(v)

    # Value extraction with type specified
    f = vtk.vtkVariantExtract(v, 'double')

    # Casting a variant
    v = vtk.vtkVariant("10")
    i = vtk.vtkVariantCast(v, 'int')
    print("Valid cast result: %r" % i)

    # A failed cast returns None
    v = vtk.vtkVariant("hello")
    i = vtk.vtkVariantCast(v, 'int')
    print("Invalid cast result: %r" % i)

    #
    # Comparisons and sorting: See VTK docs for more info
    #

    # Special function vtk.vtkVariantStrictWeakOrder:
    # Compare variants by type first, and then by value.  For Python 2, the
    # return values are -1, 0, 1 like the Python 2 "cmp()" method.  This is
    # in contrast with the Python 3 and C++ versions of this function, which
    # check if (v1 < v2) and return True or False.
    v1 = vtk.vtkVariant(10)
    v2 = vtk.vtkVariant("10")
    r = vtk.vtkVariantStrictWeakOrder(v1, v2)
    print("Strict weak order (10, '10') ->", r)

    # Sorting by strict weak order, using a key function:
    unsorted = [1, 2.5, vtk.vtkVariant(), "0", unicodeEtre]
    l = [vtk.vtkVariant(x) for x in unsorted]
    l.sort(key=vtk.vtkVariantStrictWeakOrderKey)
    print("Sort by weak order ->", l)

    # Check two variants for strict equality of type and value.
    b = vtk.vtkVariantStrictEquality(v1, v2)
    print("Strict equality (10, '10') -> %s" % b)

    # Two special-purpose methods.
    # First is identical to (v1 < v2)
    b = vtk.vtkVariantLessThan(v1, v2)
    # Second is identical to (v1 == v2)
    b = vtk.vtkVariantEqual(v1, v2)