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?

Answer 1

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