# PythonPlot.streamplot error

**URL:** <https://discourse.julialang.org/t/pythonplot-streamplot-error/136365>\
**Category:** Visualization\
**Tags:** pythonplot\
**Created:** [March 24, 2026, 3:28pm UTC](https://discourse.julialang.org/t/pythonplot-streamplot-error/136365 "2026-03-24T15:28:28Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![Wen-Wei\_Tseng](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/wen-wei_tseng/32/28839_2.png) [@Wen-Wei\_Tseng](https://discourse.julialang.org/u/Wen-Wei_Tseng)\
**Post date:** [March 24, 2026, 3:28pm UTC](https://discourse.julialang.org/t/pythonplot-streamplot-error/136365/1 "2026-03-24T15:28:28Z")

</div>

Hello, I was trying to generate a stream plot using PythonPlot.jl like this example: [Julia\_Examples/pyplot\_streamplot.jl at master · gizmaa/Julia\_Examples · GitHub](https://github.com/gizmaa/Julia_Examples/blob/master/pyplot_streamplot.jl)

However, I was encounter an error while running the following code. I would like to know how to correctly call `streamplot()` under PythonPlot.jl .

```julia
using PythonPlot

## This works
x = range(0; stop=2*pi, length=1000)
y = sin.(3 * x + 4 * cos.(2 * x))
plot(x, y, color="red", linewidth=2.0, linestyle="--")
title("A sinusoidally modulated sinusoid")
gcf()

#---
minval = -3
maxval = 3
steps = 100
X = repeat(range(minval,stop=maxval,length=steps)',steps)
Y = repeat(range(minval,stop=maxval,length=steps),1,steps)
U = -1 .- X.^2 .+ Y
V = 1 .+ X .- Y.^2
speed = sqrt.(U.^2 .+ V.^2)

fig = figure("pyplot_streamplot",figsize=(10,10))
subplot(311)
streamplot(X,Y,U,V) ## This line gives error

```

Error message:

```julia-auto
ERROR: Python: Julia: an error occurred while setting an error
Python stacktrace:
 [1] __getitem__
   @ C:\Users\sosiristseng\.julia\packages\PythonCall\83z4q\src\JlWrap\array.jl:350
 [2] __init__
   @ matplotlib.streamplot d:\github\mmsb-bebi-5009\.CondaPkg\.pixi\envs\default\Lib\site-packages\matplotlib\streamplot.py:329
 [3] streamplot
   @ matplotlib.streamplot d:\github\mmsb-bebi-5009\.CondaPkg\.pixi\envs\default\Lib\site-packages\matplotlib\streamplot.py:91
 [4] inner
   @ matplotlib d:\github\mmsb-bebi-5009\.CondaPkg\.pixi\envs\default\Lib\site-packages\matplotlib\ __init__.py:1524
 [5] streamplot
   @ matplotlib.pyplot d:\github\mmsb-bebi-5009\.CondaPkg\.pixi\envs\default\Lib\site-packages\matplotlib\pyplot.py:4141
Stacktrace:
 [1] pythrow()
   @ PythonCall.Core C:\Users\sosiristseng\.julia\packages\PythonCall\83z4q\src\Core\err.jl:77
 [2] errcheck
   @ C:\Users\sosiristseng\.julia\packages\PythonCall\83z4q\src\Core\err.jl:10 [inlined]
 [3] pycallargs(f::PythonCall.Py, args::PythonCall.Py)
   @ PythonCall.Core C:\Users\sosiristseng\.julia\packages\PythonCall\83z4q\src\Core\builtins.jl:194
 [4] pycall(::PythonCall.Py, ::Matrix{Float64}, ::Vararg{Matrix{Float64}}; kwargs::@Kwargs{})
   @ PythonCall.Core C:\Users\sosiristseng\.julia\packages\PythonCall\83z4q\src\Core\builtins.jl:213
 [5] pycall(::PythonCall.Py, ::Matrix{Float64}, ::Vararg{Matrix{Float64}})
   @ PythonCall.Core C:\Users\sosiristseng\.julia\packages\PythonCall\83z4q\src\Core\builtins.jl:203
 [6] streamplot(::Matrix{Float64}, ::Vararg{Matrix{Float64}}; kws::@Kwargs{})
   @ PythonPlot C:\Users\sosiristseng\.julia\packages\PythonPlot\oS8x4\src\PythonPlot.jl:179
 [7] streamplot(::Matrix{Float64}, ::Vararg{Matrix{Float64}})
   @ PythonPlot C:\Users\sosiristseng\.julia\packages\PythonPlot\oS8x4\src\PythonPlot.jl:175
 [8] top-level scope
   @ d:\github\mmsb-bebi-5009\test.jl:22

```

System info

```julia-auto
Julia Version 1.12.5
OS: Windows 11 24H2

```

Installed packages

```julia-auto
  [274fc56d] + PythonPlot v1.0.6

```

Manifest

```julia-auto
  [3da002f7] + ColorTypes v0.12.1
  [5ae59095] + Colors v0.13.1
  [992eb4ea] + CondaPkg v0.2.34
  [9a962f9c] + DataAPI v1.16.0
  [e2d170a0] + DataValueInterfaces v1.0.0
  [53c48c17] + FixedPointNumbers v0.8.5
  [82899510] + IteratorInterfaceExtensions v1.0.0
  [692b3bcd] + JLLWrappers v1.7.1
  [682c06a0] + JSON v1.4.0
  [b964fa9f] + LaTeXStrings v1.4.0
  [1914dd2f] + MacroTools v0.5.16
  [0b3b1443] + MicroMamba v0.1.15
  [bac558e1] + OrderedCollections v1.8.1
  [69de0a69] + Parsers v2.8.3
  [fa939f87] + Pidfile v1.3.0
  [aea7be01] + PrecompileTools v1.3.3
  [21216c6a] + Preferences v1.5.2
  [6099a3de] + PythonCall v0.9.31
  [274fc56d] + PythonPlot v1.0.6
  [189a3867] + Reexport v1.2.2
  [6c6a2e73] + Scratch v1.3.0
  [10745b16] + Statistics v1.11.1
  [ec057cc2] + StructUtils v2.7.1
  [3783bdb8] + TableTraits v1.0.1
  [bd369af6] + Tables v1.12.1
  [e17b2a0c] + UnsafePointers v1.0.0
  [81def892] + VersionParsing v1.3.0
  [f8abcde7] + micromamba_jll v2.3.1+0
  [4d7b5844] + pixi_jll v0.41.3+0
  [0dad84c5] + ArgTools v1.1.2
  [56f22d72] + Artifacts v1.11.0
  [2a0f44e3] + Base64 v1.11.0
  [ade2ca70] + Dates v1.11.0
  [f43a241f] + Downloads v1.7.0
  [7b1f6079] + FileWatching v1.11.0
  [b77e0a4c] + InteractiveUtils v1.11.0
  [ac6e5ff7] + JuliaSyntaxHighlighting v1.12.0
  [4af54fe1] + LazyArtifacts v1.11.0
  [b27032c2] + LibCURL v0.6.4
  [76f85450] + LibGit2 v1.11.0
  [8f399da3] + Libdl v1.11.0
  [37e2e46d] + LinearAlgebra v1.12.0
  [56ddb016] + Logging v1.11.0
  [d6f4376e] + Markdown v1.11.0
  [ca575930] + NetworkOptions v1.3.0
  [44cfe95a] + Pkg v1.12.1
  [de0858da] + Printf v1.11.0
  [9a3f8284] + Random v1.11.0
  [ea8e919c] + SHA v0.7.0
  [9e88b42a] + Serialization v1.11.0
  [6462fe0b] + Sockets v1.11.0
  [f489334b] + StyledStrings v1.11.0
  [fa267f1f] + TOML v1.0.3
  [a4e569a6] + Tar v1.10.0
  [8dfed614] + Test v1.11.0
  [cf7118a7] + UUIDs v1.11.0
  [4ec0a83e] + Unicode v1.11.0
  [e66e0078] + CompilerSupportLibraries_jll v1.3.0+1
  [deac9b47] + LibCURL_jll v8.15.0+0
  [e37daf67] + LibGit2_jll v1.9.0+0
  [29816b5a] + LibSSH2_jll v1.11.3+1
  [14a3606d] + MozillaCACerts_jll v2025.11.4
  [4536629a] + OpenBLAS_jll v0.3.29+0
  [458c3c95] + OpenSSL_jll v3.5.4+0
  [83775a58] + Zlib_jll v1.3.1+2
  [8e850b90] + libblastrampoline_jll v5.15.0+0
  [8e850ede] + nghttp2_jll v1.64.0+1
  [3f19e933] + p7zip_jll v17.7.0+0

```

---

<div class="post-metadata">

**Author:** ![Benny](https://avatars.discourse-cdn.com/v4/letter/b/49beb7/32.png) [@Benny](https://discourse.julialang.org/u/Benny)\
**Post date:** [March 26, 2026, 12:57am UTC](https://discourse.julialang.org/t/pythonplot-streamplot-error/136365/2 "2026-03-26T00:57:00Z")

</div>

`streamplot` seems to be erroring at array slicing for checking row equality in a matrix (`elif np.ndim(x) == 2: x_row = x[0]` at [line 329](https://github.com/matplotlib/matplotlib/blob/1392cbe3c79cdb93f9282747841d648770f60249/lib/matplotlib/streamplot.py#L329) of streamplot.py), which is fairly concerning for `PythonCall.ArrayValue` wrapping a plain `Matrix{Float64}`. Not sure how that’s going wrong, maybe somewhere translating the [array indices](https://github.com/JuliaPy/PythonCall.jl/blob/be1634298ff27633bc3b4ce414526100bad2fe2c/src/JlWrap/array.jl#L65) from Python to Julia.

`streamplot` used to only support 1D arrays, which should dodge that particular check. Try these edits, maybe nothing else goes wrong:

```julia-auto
Xrange = range(minval,stop=maxval,length=steps)
X = Xrange'
Y = range(minval,stop=maxval,length=steps)

```

and:

```julia-auto
streamplot(Xrange, Y, U, V)

```

EDIT: Looked into this a bit further, and the indexing issue is an intentional limitation. The automatic `juliacall.ArrayValue` on the Python side does adjust Python’s 0-based indexing and slicing syntax for the wrapped Julia `AbstractArray`; for example, `@pyexec X => "print(X[0,:])"` works and indexes `X[1,:]`. However, wrapping a Julia `AbstractArray` cannot be entirely the same as a NumPy array; in this case, Julia `AbstractArray`s and NumPy arrays disagree on omitted trailing indices and linear indexing, so `@pyexec X => "print(X[0])"` fails. Not sure how that script worked before, but in the general case, you need to rewrap [in a NumPy array](https://juliapy.github.io/PythonCall.jl/stable/faq/#Issues-when-Numpy-arrays-are-expected).

---

<div class="post-metadata">

**Author:** ![Wen-Wei\_Tseng](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/wen-wei_tseng/32/28839_2.png) [@Wen-Wei\_Tseng](https://discourse.julialang.org/u/Wen-Wei_Tseng)\
**Post date:** [March 31, 2026, 8:56am UTC](https://discourse.julialang.org/t/pythonplot-streamplot-error/136365/3 "2026-03-31T08:56:52Z")

</div>

@Benny Thank you for your clear explanation. Your solution works!