Hi @rgommers @ngoldbaum,

This issue is meant for monitoring and discussing cleanup of np.lib namespace. (Tracking parent issue: #23999)

Main goal is to make each public function, which lives in np.lib, available either from the main namespace np or "local lib" namespace e.g. np.lib.npyio. As a result, there will be only one way to access a specific public function in NumPy.
To achieve it, for each relevant lib submodule, there will be a private file (that starts with _) imported by the main namespace, and a public file that allows to be accessed as a public submodule.

# Example:

np.broadcast_to  # imported from numpy/lib/_stride_tricks.py

np.lib.stride_tricks.normalize_axis_tuple  # imported from numpy/lib/stride_tricks.py

Let's call this mechanism "main or submodule namespace access". (maybe a better name?)

The scope of the milestone:

"ns" stands for "namespace". ☑️ means that this submodule has been refactored.

• lib PR
  main ns: N/A
  local ns: NumpyVersion, Arrayterator, add_newdoc, add_docstring, tracemalloc_domain
• array_utils PR
  main ns: N/A
  local ns: byte_bounds, discover_array_parameters, normalize_axis_index, normalize_axis_tuple
• histograms PR
  main ns: histogram, histogramdd, histogram_bin_edges
  local ns:
• type_check PR
  main ns: iscomplexobj, isrealobj, imag, iscomplex, isreal, nan_to_num, real, real_if_close, typename, mintypecode, common_type
  local ns:
• nanfunctions PR
  main ns: nansum, nanmax, nanmin, nanargmax, nanargmin, nanmean, nanmedian, nanpercentile, nanvar, nanstd, nanprod, nancumsum, nancumprod, nanquantile
  local ns:
• function_base PR
  main ns: select, piecewise, trim_zeros, copy, iterable, percentile, diff, gradient, angle, unwrap, sort_complex, flip, rot90, extract, place, vectorize, asarray_chkfinite, average, bincount, digitize, cov, corrcoef, median, sinc, hamming, hanning, bartlett, blackman, kaiser, i0, meshgrid, delete, insert, append, interp, quantile
  local ns:
• shape_base PR
  main ns: column_stack, row_stack, dstack, array_split, split, hsplit, vsplit, dsplit, apply_over_axes, expand_dims, apply_along_axis, kron, tile, get_array_wrap, take_along_axis, put_along_axis
  local ns:
• arraypad PR
  main ns: pad
  local ns:
• arraysetops PR
  main ns: ediff1d, intersect1d, setxor1d, union1d, setdiff1d, unique, isin
  local ns:
• twodim_base PR
  main ns: diag, diagflat, eye, fliplr, flipud, tri, triu, tril, vander, histogram2d, mask_indices, tril_indices, tril_indices_from, triu_indices, triu_indices_from
  local ns:
• ufunclike PR
  main ns: fix, isneginf, isposinf
  local ns:
• utils PR
  main ns: get_include, info, show_runtime
  local ns:
• npyio PR
  main ns: savetxt, loadtxt, genfromtxt, load, save, savez, savez_compressed, packbits, unpackbits, fromregex,
  local ns: DataSource, NpzFile, BagObj
• polynomial PR
  main ns: poly, roots, polyint, polyder, polyadd, polysub, polymul, polydiv, polyval, poly1d, polyfit
  local ns:
• stride_tricks PR
  main ns: broadcast_to, broadcast_arrays, broadcast_shapes
  local ns: as_strided, sliding_window_view
• index_tricks PR
  main ns: diag_indices_from, diag_indices, fill_diagonal, ndindex, ndenumerate, ix_, ogrid, mgrid, unravel_index, ravel_multi_index, s_, c_, r_, index_exp
  local ns:

This work should be less disturbing than main namespace cleanup, as I think a function is rarely imported from np.lib if it's already available in np.