Import a module in Python only if it doesn't already exist

Question

I want to use a module, e.g. BeautifulSoup, in my Python code, so I usually add this to the top of the file:

from BeautifulSoup import BeautifulSoup

However, when I distribute the module I'm writing, others may not have BeautifulSoup, so I'll just include it in my directory structure like so:

Mode                LastWriteTime     Length Name
----                -------------     ------ ----
d----         9/19/2011   5:45 PM            BeautifulSoup
-a---         9/17/2011   8:06 PM       4212 myscript.py

Now, my modified myscript.py file will look like this at the top to reference the local copy of BeautifulSoup:

from BeautifulSoup.BeautifulSoup import BeautifulSoup, CData

But what if the developer who uses my library already has BeautifulSoup installed on their machine? I want to modify myscript.py so that it checks to see if BeautifulSoup is already installed, and if so, use the standard module. Otherwise, use the included one.

Using Pseudo-python:

if fBeautifulSoupIsInstalled:
    from BeautifulSoup import BeautifulSoup, CData
else:
    from BeautifulSoup.BeautifulSoup import BeautifulSoup, CData

Is this possible? If so, how?

Taken from effbot.org/zone/import-confusion.htm : When Python imports a module, it first checks the module registry (sys.modules) to see if the module is already imported. If that’s the case, Python uses the existing module object as is. — mal-wan
– mal-wan, Commented Sep 19, 2011 at 22:33
Try to import it. If it doesn't work, catch the ImportError and import from your local copy. Name your local copy something else (myBeautifulSoup) so it doesn't hide the user installed module. — Steven Rumbalski
– Steven Rumbalski, Commented Sep 19, 2011 at 22:38
@mwan: Ben doesn't need to know if it's already imported, he needs to know if it's already on the system. — Ethan Furman
– Ethan Furman, Commented Sep 19, 2011 at 23:27

Mikko Ohtamaa · Accepted Answer · 2011-09-19 22:35:41Z

16

Usually the following pattern is used to handle this situation in Python.

First rename your BeautifulSoup module something else, e.g. MyBeautifulSoup

Then:

try:
    import BeautifulSoup # Standard
except ImportError:
    import MyBeautifulSoup as BeautifulSoup # internal distribution

answered Sep 19, 2011 at 22:35

Mikko Ohtamaa

84.9k63 gold badges296 silver badges478 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Import a module in Python only if it doesn't already exist

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related