Using pip to install python dependencies for Julia.

build.jl

using PyCall

# Change that to whatever packages you need.
const PACKAGES = ["pyyaml"]

# Import pip
try
    @pyimport pip
catch
    # If it is not found, install it
    get_pip = joinpath(dirname(@__FILE__), "get-pip.py")
    download("https://bootstrap.pypa.io/get-pip.py", get_pip)
    run(`$(PyCall.python) $get_pip --user`)
end

@pyimport pip
args = UTF8String[]
if haskey(ENV, "http_proxy")
    push!(args, "--proxy")
    push!(args, ENV["http_proxy"])
end
push!(args, "install")
push!(args, "--user")
append!(args, PACKAGES)

pip.main(args)

Hello, how to use this file ? Is it necessary to put it somewhere and it will be automatically executed when an user install my package ?
My package depends upon a python package that is not available in conda (but it is trough pip) and I don' know where to start to guarantee its presence to users..

You need to put this file as your package deps/build.jl file, that will be run when someone install this package.

I've tried this and the @pyimport pip fails on Travis, it then tries to install PIP and decides it already exists. Any idea?

Calling pip.main does not works at least as of pip v19.0.3, but probably starting around v10. See https://stackoverflow.com/questions/12332975/installing-python-module-within-code. Here's what I do instead:

import PyCall: pyimport

# See https://stackoverflow.com/questions/12332975/installing-python-module-within-code.
const PIP_PACKAGES = ["taichi", "matplotlib"]

sys = pyimport("sys")
subprocess = pyimport("subprocess")
subprocess.check_call([sys.executable, "-m", "pip", "install", "--user", "--upgrade", "--force-reinstall", PIP_PACKAGES...])