Mathematica Asked on March 7, 2021
I am trying to use ExternalEvaluate for a Python session. For some reason I cannot import a file from there that I can import successfully when I call python some other way. I already verified that the current working directory in python is the correct one. I also added the directory to the path in two ways because it solved a similar issue here https://mathematica.stackexchange.com/a/185587/45020. For example the following outputs the correct directory (twice) and indeed the file I am trying to load is listed in the os.listdir() output.
SetDirectory[NotebookDirectory[]]
s = StartExternalSession["Python"];
ExternalEvaluate[s, "import os"];
ExternalEvaluate[s, "os.getcwd()"]
ExternalEvaluate[s, "os.chdir(" <> Directory[] <> ")"];
ExternalEvaluate[s, "sys.path.insert(1, '')"];
ExternalEvaluate[s, "os.getcwd()"]
ExternalEvaluate[s, "sys.path.insert(os.getcwd())"];
ExternalEvaluate[s, "os.listdir()"]
ExternalEvaluate[s, "import filenameWithoutPYExtension"]
I still get the no module named 'filenameWithoutPYExtension' error though.
In Mathematica 12.2 Directory[] returns the Documents folder in windows, instead of that use NotebookDirectory[] to get your notebook directory. In python, for importing files from unknown directories you can use sys library:
s = StartExternalSession["Python"];
ExternalEvaluate[s,
"import sys;sys.path.append(" <>
ExportString[NotebookDirectory[], "PythonExpression"] <> ")"]
ExternalEvaluate[s, "import filenameWithoutPYExtension"]
DeleteObject[s];
Also see this post.
Another point is you can use ; to run multiple lines in python:
ExternalEvaluate["Python", "import os;os.getcwd()"]
(*Out: "C:UsersUSERNAMEDocuments" *)
While passing strings to python directly, having single is problematic, for this reason, I use ToString[..., InputForm] which replace with . Using ExportString[..., "PythonExpression"] is a better option so I replace it with that.
Answered by Beny Izd on March 7, 2021
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