howto check does module 'asdf' exist? (is available for import)

[dmitrey]

howto check does module 'asdf' exist (is available for import) or no?
(without try/cache of course)
Thx in advance, D.

 

[Stefan Behnel]

howto check does module 'asdf' exist (is available for import) or no?

Walk through sys.path and find it yourself?

(without try/cache of course)

Why is the obvious (and most common) try/import/catch solution "of course" out?

Stefan

 

[js]

Why not just use try?
Trying to import a module is a python idiom.
http://www.diveintopython.org/file_handling/index.html

 

[Asun Friere]

howto check does module 'asdf' exist (is available for import) or no?

try :
import asdf
del asdf
except ImportError :
#do stuff ...

(without try/cache of course)

Oops sorry, you didn't want it the obvious way ... but why ever not?

 

[Asun Friere]

howto check does module 'asdf' exist (is available for import) or no?

try :
import asdf
del asdf
except ImportError :
print "module asdf not available"
else :
print "module asdf available for loading"

You can generalise this, but at the expense of a couple of exec
statements:
def is_module_available (module) :
try :
exec('import %s' % module)
exec('del %s' % module)
except ImportError :
return False
else :
return True

(without try/cache of course)

Oops sorry, you wanted it done in some non-obvious way! Why?!

 

[Carsten Haese]

You can generalise this, but at the expense of a couple of exec
statements:
def is_module_available (module) :
try :
exec('import %s' % module)
exec('del %s' % module)
except ImportError :
return False
else :
return True

You can save the exec statement by using the built-in __import__
function:

def is_module_available(modulename):
try: mod = __import__(modulename)
except ImportError: return False
else: return True

 

[Paul Rubin]

try :
import asdf
del asdf
except ImportError :
print "module asdf not available"
else :
print "module asdf available for loading"

But this has a side effect: if asdf is already loaded, it deletes it.

 

[kaens]

I think that's there because you just wanted to check if it was
available for import, implying that you didn't actually want to import
it right then.

 

[Paul Rubin]

I think that's there because you just wanted to check if it was
available for import, implying that you didn't actually want to import
it right then.

Whether it's available for import and whether you've already imported
it are two separate questions. Maybe you said "import fghj as asdf"
and now you want to find out if there's another module actually named
asdf. It would be cleaner if there's a method with no side effects.