class_docstr: Translates slice objects to concatenation along an axis.
  
  For detailed documentation on usage, see `r_`.
class_docstr_tok: ["Translates","slice","objects","to","concatenation","along","an","axis",".","For","detailed","documentation","on","usage",",","see","`","r_","`","."]
code: def __getitem__(self, key):
      # handle matrix builder syntax
      if isinstance(key, str):
          frame = sys._getframe().f_back
          mymat = matrixlib.bmat(key, frame.f_globals, frame.f_locals)
          return mymat
  
      if not isinstance(key, tuple):
          key = (key,)
  
      # copy attributes, since they can be overridden in the first argument
      trans1d = self.trans1d
      ndmin = self.ndmin
      matrix = self.matrix
      axis = self.axis
  
      objs = []
      scalars = []
      arraytypes = []
      scalartypes = []
  
      for k, item in enumerate(key):
          scalar = False
          if isinstance(item, slice):
              step = item.step
              start = item.start
              stop = item.stop
              if start is None:
                  start = 0
              if step is None:
                  step = 1
              if isinstance(step, complex):
                  size = int(abs(step))
                  newobj = linspace(start, stop, num=size)
              else:
                  newobj = _nx.arange(start, stop, step)
              if ndmin > 1:
                  newobj = array(newobj, copy=False, ndmin=ndmin)
                  if trans1d != -1:
                      newobj = newobj.swapaxes(-1, trans1d)
          elif isinstance(item, str):
              if k != 0:
                  raise ValueError(
                      "special directives must be the " "first entry."
                  )
              if item in ("r", "c"):
                  matrix = True
                  col = item == "c"
                  continue
              if "," in item:
                  vec = item.split(",")
                  try:
                      axis, ndmin = [int(x) for x in vec[:2]]
                      if len(vec) == 3:
                          trans1d = int(vec[2])
                      continue
                  except Exception:
                      raise ValueError("unknown special directive")
              try:
                  axis = int(item)
                  continue
              except (ValueError, TypeError):
                  raise ValueError("unknown special directive")
          elif type(item) in ScalarType:
              newobj = array(item, ndmin=ndmin)
              scalars.append(len(objs))
              scalar = True
              scalartypes.append(newobj.dtype)
          else:
              item_ndim = ndim(item)
              newobj = array(item, copy=False, subok=True, ndmin=ndmin)
              if trans1d != -1 and item_ndim < ndmin:
                  k2 = ndmin - item_ndim
                  k1 = trans1d
                  if k1 < 0:
                      k1 += k2 + 1
                  defaxes = list(range(ndmin))
                  axes = defaxes[:k1] + defaxes[k2:] + defaxes[k1:k2]
                  newobj = newobj.transpose(axes)
          objs.append(newobj)
          if not scalar and isinstance(newobj, _nx.ndarray):
              arraytypes.append(newobj.dtype)
  
      # Ensure that scalars won't up-cast unless warranted
      final_dtype = find_common_type(arraytypes, scalartypes)
      if final_dtype is not None:
          for k in scalars:
              objs[k] = objs[k].astype(final_dtype)
  
      res = self.concatenate(tuple(objs), axis=axis)
  
      if matrix:
          oldndim = res.ndim
          res = self.makemat(res)
          if oldndim == 1 and col:
              res = res.T
      return res
  
imports: from __future__ import division, absolute_import, print_function
  import functools
  import sys
  import math
  import numpy.core.numeric
  from numpy.core.numeric import asarray, ScalarType, array, alltrue, cumprod, arange, ndim
  from numpy.core.numerictypes import find_common_type, issubdtype
  import numpy.matrixlib
  from .function_base import diff
  from numpy.core.multiarray import ravel_multi_index, unravel_index
  from numpy.core.overrides import set_module
  from numpy.core import overrides, linspace
  from numpy.lib.stride_tricks import as_strided
label_desc: Use image node_id 2 for calling the AxisConcatenator obj's underlying member method code with example usage: obj.__getitem__(key) and returns: res, mymat