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

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

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

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

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

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

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

modules = set(["sys", "os", "jinja"])
try:
  for module in modules:
    __import__(module)
  doSomething()
except ImportError, e:
    print e