Install a package and import in the same python script

Question

(Edit: I made a typo when writing this question: I put quotation mark around "pyparsing" in script. Thanks @dswdsyd)

When running a python script, there's only python standard library on target machine. When a package is needed, I have to install it first. For example, When I tried to install pyparsing and import it:

subprocess.call([sys.executable, "-m", "pip", "install", "pyparsing"])    
import pyparsing

I got error:

ModuleNotFoundError: No module named 'pyparsing'

So how to install and import a package in the same python script?

[Update:] In the second run of the script, the package can be imported. Strange.

Noap, I still got "ModuleNotFoundError: No module named 'pyparsing'". — Nick
– Nick, Commented Oct 30, 2019 at 6:35
that is not reproducable , your provided code works just fine — LinPy
– LinPy, Commented Oct 30, 2019 at 6:38
Can you catch the stdout and stderr of the subprocess call and provide it? — FlyingTeller
– FlyingTeller, Commented Oct 30, 2019 at 10:29
subprocess works fine. Only import doesn't work at the first run. It works in a second run. — Nick
– Nick, Commented Oct 30, 2019 at 11:31

Community · Accepted Answer · 2020-06-20 09:12:55Z

2

Problem solved by importlib.invalidate_caches(). According to importlib's documentation:

importlib.invalidate_caches()

Invalidate the internal caches of finders stored at sys.meta_path. If a finder implements invalidate_caches() then it will be called to perform the invalidation. This function should be called if any modules are created/installed while your program is running to guarantee all finders will notice the new module’s existence.

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Oct 31, 2019 at 2:14

Nick

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Comments

dswdsyd · Accepted Answer · 2019-10-30 06:18:50Z

1

Essentially you are passing pyparsing as a variable instead of a string, to fix this change pyparsing to "pyparsing"

try this:

import subprocess
import sys
subprocess.call([sys.executable, "-m", "pip", "install", "pyparsing"])    
import pyparsing

answered Oct 30, 2019 at 6:18

dswdsyd

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1 Comment

Nick Over a year ago

Ah my bad, thank you. I indeed put quotation mark around "pyparsing". The same error occur again.

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