not getting output from parmiko/ssh command

I am using paramiko/ssh/python to attempt to run a command on a remote server. When I ssh manually and run the command in question, I get the results I want. But if I use the python (co-opted from another thread on this site) below, there is no returned data. If I modify the command to be something more basic like 'pwd' or 'ls' I can then get the output. Any help is appreciated.

Thanks, Matt

import paramiko  
import time  
import sys, os, select  
import select  
hostname='10.15.27.166'  
hostport=22  
cmd='tail -f /x/web/mlog.txt' #works  
#cmd='customexe -args1 -args2' #doesn't work  
client = paramiko.SSHClient()  
client.load_system_host_keys()  
client.connect(hostname=hostname, username=username, password=password)  
transport = client.get_transport()  
channel = transport.open_session()  
channel.exec_command(cmd)  
while True:  
  rl, wl, xl = select.select([channel],[],[],0.0)  
  if len(rl) > 0:  
    # Must be stdout  
    print channel.recv(1024)  
  time.sleep(1)

I found a fix, though not necessarily the root cause: When paramiko created the ssh connection, it did not run my bash_profile in my home directory on the remote server. So, I copied the commands from the bash_profile into the cmd variable and thus loaded various environment variables that I thought would have loaded automatically. Then the command "customexe ..." returned output as expected.