parsing python code

[les]

Hi,
i would like to find out the function call tree of a python
code. i.e.
say i have a code like this:
def fun111():
   ..
def fun11():
   fun111()
  
def fun1():
   fun11()
   fun12()

if __name__ =='__main__':
    fun1()
then i would like to build a dictionary like this

d ={ 'root': '__name__',
      '__name__': ['fun1']
      'fun1': [ 'fun11','fun12'],
      'fun11': [ 'fun111']
   }

it is easy to parse out function names from the code,
but not so easy to jump around to figure the tree structure.
is there a module which exports some function when
given a functionname returns all the functions it calls?
(only those functions that are in the source code)

so far i have something like this
that removes the function names
but before i try the brute force way,i wanted to ask if there is already 
a module that does what i want

######################################
from sys import argv,exit,stdin


if __name__ == '__main__':
	try:
		codefile = argv[1]
	except IndexError:
		print 'USAGE %s <file>' % argv[0]
	        exit(-1)
        #pull out function names
	fp = open(codefile)
	fun_names=[]
	for x in fp:
		if x[0:3]=='def':
			fun_names.append( x.split()[1].split('(')[0])
	print fun_names
	fp.close()
	# go thought the file again and build nested list
	nested={}
	fp = open(codefile)
	
        ################ I NEED HELP HERE
	
	fp.close()

thanks