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IronPython: System.Array

When you start interop'ing with .NET in IronPython, sooner or later, you will find that you are in need of creating an array as argument. There are mainly 2 ways to create array objects:

  • Array with type indexing (for one-dimensional array object only), and
  • classic reflection API: Array.CreateInstance

System.Array indexing with a type creates a concrete array type, which can then take a collection of the element objects (or an enumerable) and form the array object. There are half dozen Array.CreateInstance overloads, which allow us to create one-dimensional empty array, also multi-dimensional/non-zero lower-bound arrays.

 import System
array_int = System.Array[int]
print array_int               # <type 'Array[int]'>

# list
print array_int([1, 2])       # System.Int32[](1, 2)
# tuple
print array_int((3, 4, 5))    # System.Int32[](3, 4, 5)
# xrange
print array_int(xrange(6,10)) # System.Int32[](6, 7, 8, 9)
# CLR List
print array_int(System.Collections.Generic.List[int]()) # System.Int32[]()

# one-dimensional array 
a1 = System.Array.CreateInstance(int, 5)
for i in range(5): a1[i] = i * 10
print a1        # System.Int32[](0, 10, 20, 30, 40)

# two-dimensional array 
a2 = System.Array.CreateInstance(float, 2, 2)
a2[1, 1] = 3.14
print a2        # System.Double[,](
                # 0.0, 0.0
                # 0.0, 3.14)

IronPython also supports some python list-like operation to the CLR array objects, such as indexing with slice, +, *, in...

 a1 = array_int(range(5))
a2 = array_int([100])

# slice
print a1[1:-1]      # System.Int32[](1, 2, 3)
# +
print a1 + a2       # System.Int32[](0, 1, 2, 3, 4, 100)
# *
print a1 * 2        # System.Int32[](0, 1, 2, 3, 4, 0, 1, 2, 3, 4)
# +, upcast the result to object[]
print a2 + System.Array[str]('py')  # System.Object[](100, 'p', 'y')

# slice with step
print a1[1::2]      # System.Int32[](1, 3)
# assignment 
a1[1::2] = [11, 13]
print a1            # System.Int32[](0, 11, 2, 13, 4)

# in/__contains__
print 11 in a1      # True

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