Do we use try,except in every single function?

Should we always enclose every function we write with a try...except block? I ask this because sometimes in one function we raise Exception, and the caller that calls this function doesn't have exception

def caller():
   stdout, stderr = callee(....)


def callee():
   ....
    if stderr:
       raise StandardError(....)

then our application crash. In this obvious case, I am tempted to enclose callee and caller with try..except.

But I've read so many Python code and they don't do these try..block all the time.

def cmd(cmdl):
    try:
        pid = Popen(cmdl, stdout=PIPE, stderr=PIPE)
    except Exception, e:
        raise e
    stdout, stderr = pid.communicate()
    if pid.returncode != 0:
        raise StandardError(stderr)
    return (stdout, stderr)

def addandremove(*args,**kwargs):
    target = kwargs.get('local', os.getcwd())
    f = kwargs.get('file', None)
    vcs = kwargs.get('vcs', 'hg')

    if vcs is "hg":
        try:
            stdout, stderr = cmd(['hg', 'addremove', '--similarity 95'])
        except StandardError, e:
            // do some recovery
        except Exception, e:
            // do something meaningful
    return True

The real thing that bothers me is this:

If there is a 3rd function that calls addandremove() in one of the statements, do we also surround the call with a try..except block? What if this 3rd function has 3 lines, and each function calls itself has a try-except? I am sorry for building this up. But this is the sort of problem I don't get.