Return a list of imported Python modules used in a script?

IMO the best way todo this is to use the http://furius.ca/snakefood/ package. The author has done all of the required work to get not only directly imported modules but it uses the AST to parse the code for runtime dependencies that a more static analysis would miss.

Worked up a command example to demonstrate:

sfood ./example.py | sfood-cluster > example.deps

That will generate a basic dependency file of each unique module. For even more detail use:

sfood -r -i ./example.py | sfood-cluster > example.deps

To walk a tree and find all imports, you can also do this in code:
Please NOTE – The AST chunks of this routine were lifted from the snakefood source which has this copyright: Copyright (C) 2001-2007 Martin Blais. All Rights Reserved.

 import os
 import compiler
 from compiler.ast import Discard, Const
 from compiler.visitor import ASTVisitor

 def pyfiles(startPath):
     r = []
     d = os.path.abspath(startPath)
     if os.path.exists(d) and os.path.isdir(d):
         for root, dirs, files in os.walk(d):
             for f in files:
                 n, ext = os.path.splitext(f)
                 if ext == '.py':
                     r.append([d, f])
     return r

 class ImportVisitor(object):
     def __init__(self):
         self.modules = []
         self.recent = []
     def visitImport(self, node):
         self.accept_imports()
         self.recent.extend((x[0], None, x[1] or x[0], node.lineno, 0)
                            for x in node.names)
     def visitFrom(self, node):
         self.accept_imports()
         modname = node.modname
         if modname == '__future__':
             return # Ignore these.
         for name, as_ in node.names:
             if name == '*':
                 # We really don't know...
                 mod = (modname, None, None, node.lineno, node.level)
             else:
                 mod = (modname, name, as_ or name, node.lineno, node.level)
             self.recent.append(mod)
     def default(self, node):
         pragma = None
         if self.recent:
             if isinstance(node, Discard):
                 children = node.getChildren()
                 if len(children) == 1 and isinstance(children[0], Const):
                     const_node = children[0]
                     pragma = const_node.value
         self.accept_imports(pragma)
     def accept_imports(self, pragma=None):
         self.modules.extend((m, r, l, n, lvl, pragma)
                             for (m, r, l, n, lvl) in self.recent)
         self.recent = []
     def finalize(self):
         self.accept_imports()
         return self.modules

 class ImportWalker(ASTVisitor):
     def __init__(self, visitor):
         ASTVisitor.__init__(self)
         self._visitor = visitor
     def default(self, node, *args):
         self._visitor.default(node)
         ASTVisitor.default(self, node, *args) 

 def parse_python_source(fn):
     contents = open(fn, 'rU').read()
     ast = compiler.parse(contents)
     vis = ImportVisitor() 

     compiler.walk(ast, vis, ImportWalker(vis))
     return vis.finalize()

 for d, f in pyfiles('/Users/bear/temp/foobar'):
     print d, f
     print parse_python_source(os.path.join(d, f))