Memory leak with pyplot

[gabrevaya]

When I create matplotlib.pyplot plots, the memory keeps increasing and is not released by the garbage collector. The following is the case I'm interested in (with subplots) and bellow I include a more basic MWE.

Example with subplots

using PyCall
plt = pyimport("matplotlib.pyplot")

function test_pyplot()
    for i in 1:10000
        @info i
        z = rand(4, 50)
        ẑ = rand(4, 50)
        fig, axs = plot_pyplot(z, ẑ)
    end
end

function plot_pyplot(z, ẑ)
    # plt = pyimport("matplotlib.pyplot")
    N = Int(size(z, 1)/2)
    fig, axs = plt.subplots(2, N)
    for i in 1:N
        axs[1,i].plot(z[i,:], label = "true")
        axs[1,i].plot(ẑ[i,:], label = "model")

        axs[2,i].plot(z[i+N,:], label = "true")
        axs[2,i].plot(ẑ[i+N,:], label = "predicted")

        axs[2,i].set_xlabel("time steps")
        axs[i].grid(true)
        axs[i+N].grid(true)

        axs[i+N].label_outer()
        axs[i].label_outer()
    end
    # plt.close()
    return fig, axs
end

test_pyplot()

I tried defining plt and closing it inside the plot_pyplot function (commented lines) but it doesn't solve the memory leak.

Here you have a simpler MWE:

using PyCall
plt = pyimport("matplotlib.pyplot")

plot_pyplot(z) = plt.plot(z)

function test_pyplot()
    for i in 1:1000000
        @info i
        z = rand(50)
        fig = plot_pyplot(z)
    end
end

Version info and status

julia> versioninfo()
Julia Version 1.8.2
Commit 36034abf260 (2022-09-29 15:21 UTC)
Platform Info:
  OS: macOS (arm64-apple-darwin21.3.0)
  CPU: 8 × Apple M1 Pro
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-13.0.1 (ORCJIT, apple-m1)
  Threads: 1 on 6 virtual cores

(memory_leak) pkg> st
Status `~/Documents/issues/memory_leak/Project.toml`
  [438e738f] PyCall v1.94.1

I need to use pyplot directly from PyCall.jl and not through PyPlot.jl because I need to pass the fig object to Wandb.jl. Actually, maybe I could get that object from PyPlot.jl, I didn't try that yet. But since I found the bug here, I think it can be helpful to report it anyway.

[itayass]

I had a similar issue, adding

@pyimport matplotlib
matplotlib.use("Agg")

before plotting solved the issue.