Warning on strides(a::AbstractArray) when plotting array reshaped from stridden subvector

[wsshin]

I get a warning when using pcolor on a matrix generated by reshape on a stridden subvector. For example,

using PyPlot
a = rand(10);
b = @view a[1:3:end];  # stridden subvector
c = reshape(b, 2, :);  # reshape subvector into matrix
pcolor(c)

produces the following warning:

┌ Warning: The default `strides(a::AbstractArray)` implementation is deprecated for general arrays.
│ Specialize `strides(::Base.ReshapedArray)` if `Base.ReshapedArray` indeed uses a strided representation in memory.
│ Warning: inappropriately implementing this method for an array type that does not use strided
│ storage may lead to incorrect results or segfaults.
│   caller = ip:0x0
└ @ Core :-1
┌ Warning: The default `strides(a::AbstractArray)` implementation is deprecated for general arrays.
│ Specialize `strides(::Base.ReshapedArray)` if `Base.ReshapedArray` indeed uses a strided representation in memory.
│ Warning: inappropriately implementing this method for an array type that does not use strided
│ storage may lead to incorrect results or segfaults.
│   caller = stride at abstractarray.jl:350 [inlined]
└ @ Core ./abstractarray.jl:350

If a matrix itself is stridden (instead of a vector being stridden and reshaped into a matrix), then the warning does not occur.

Here is the version information:

julia> VERSION
v"0.7.1-pre.0"

[wsshin]

Related to #380, but the specific warning message is different: #380 is about strides(::Adjoint), whereas the present warning is about strides(::Base.ReshapedArray).

[dlfivefifty]

I got it while trying to do a spy plot on a sparse matrix:

julia> spy(M)
ERROR: MethodError: no method matching strides(::SparseMatrixCSC{Float64,Int64})
Closest candidates are:
  strides(::SubArray{T,2,BlockBandedMatrices.BlockSkylineMatrix{T,LL,UU},Tuple{BlockArrays.BlockSlice{Block{1,Int64}},BlockArrays.BlockSlice{Block{1,Int64}}},false} where UU where LL where T) at /Users/sheehanolver/Projects/BlockBandedMatrices.jl/src/BlockSkylineMatrix.jl:404
  strides(::SubArray{#s148,2,BlockBandedMatrices.BlockSkylineMatrix{#s148,LL,UU},Tuple{BlockArrays.BlockSlice{#s147},BlockArrays.BlockSlice{Block{1,Int64}}},L} where L where #s147<:Union{Block{1,Int64}, BlockRange{1,Tuple{UnitRange{Int64}}}} where #s148) where {LL, UU} at /Users/sheehanolver/Projects/BlockBandedMatrices.jl/src/linalg.jl:263
  strides(::SubArray{#s148,2,BlockBandedMatrices.BlockSkylineMatrix{#s148,LL,UU},Tuple{BlockArrays.BlockSlice{BlockRange{1,Tuple{UnitRange{Int64}}}},BlockArrays.BlockSlice{BlockArrays.BlockIndexRange{1,Tuple{UnitRange{Int64}}}}},L} where L where #s148) where {LL, UU} at /Users/sheehanolver/Projects/BlockBandedMatrices.jl/src/linalg.jl:283
  ...
Stacktrace:
 [1] stride(::SparseMatrixCSC{Float64,Int64}, ::Int64) at ./abstractarray.jl:342
 [2] array2py(::SparseMatrixCSC{Float64,Int64}, ::Int64, ::Int64) at /Users/sheehanolver/.julia/packages/PyCall/0jMpb/src/conversions.jl:313
 [3] array2py at /Users/sheehanolver/.julia/packages/PyCall/0jMpb/src/conversions.jl:325 [inlined]
 [4] Type at /Users/sheehanolver/.julia/packages/PyCall/0jMpb/src/conversions.jl:327 [inlined]
 [5] _pycall!(::PyCall.PyObject, ::PyCall.PyObject, ::Tuple{SparseMatrixCSC{Float64,Int64}}, ::Int64, ::Ptr{Nothing}) at /Users/sheehanolver/.julia/packages/PyCall/0jMpb/src/pyfncall.jl:24
 [6] #pycall#88 at /Users/sheehanolver/.julia/packages/PyCall/0jMpb/src/pyfncall.jl:11 [inlined]
 [7] pycall at /Users/sheehanolver/.julia/packages/PyCall/0jMpb/src/pyfncall.jl:86 [inlined]
 [8] #spy#108(::Base.Iterators.Pairs{Union{},Union{},Tuple{},NamedTuple{(),Tuple{}}}, ::Function, ::SparseMatrixCSC{Float64,Int64}) at /Users/sheehanolver/.julia/packages/PyPlot/fZuOQ/src/PyPlot.jl:179
 [9] spy(::SparseMatrixCSC{Float64,Int64}) at /Users/sheehanolver/.julia/packages/PyPlot/fZuOQ/src/PyPlot.jl:176
 [10] top-level scope at none:0

[stevengj]

Closed by JuliaPy/PyCall.jl#653