Test for Python module dependencies being installed

Question

How could one test whether a set of modules is installed, given the names of the modules. E.g.

modules = set(["sys", "os", "jinja"])

for module in modules:
  # if test(module exists):
  #   do something

While it's possible to write out the tests as:

try:
  import sys
except ImportError:
  print "No sys!"

This is a bit cumbersome for what I'm doing. Is there a dynamic way to do this?

I've tried eval("import %s"%module) but that complained of a compile error.

I'm grateful for your thoughts and suggestions. Thank you.

Answer 1

You can use the __import__() function like this::

for module in modules:
    try:
        __import__(module)
    except ImportError:
        do_something()

You can also use imp.find_module to determine whether a module can be found without importing it::

import imp
for module in modules:
    try:
        imp.find_module(module)
    except ImportError:
        do_something()

Oh, and the reason you can't use eval() is because import is a statement, not an expression. You can use exec if you really want to, though I wouldn't recommend it::

for module in modules:
    try:
        exec 'import ' + module
    except ImportError:
        do_something()

Answer 2

What's wrong with this?

modules = set(["sys", "os", "jinja"])
for m in modules:
    try:
        __import__(m)
    except ImportError:
        # do something

The above uses the __import__ function. Also, it is strictly testing whether it exists or not - its not actually saving the import anywhere, but you could easily modify it to do that.