Need help with really elementary pexpect fragment

[Saqib Ali]

I want to write a pexpect script that simply cd's into a directory ("~/
install") and then runs a command from there. It should be so easy.
But even my cd command is failing. Can't figure out what the problem
is. The command line prompt is "[my machine name here] % "

Here is the code fragment:

    print "Spawning Expect"
    p = pexpect.spawn ('/bin/tcsh',)

    print "Sending cd command"
    i = p.expect([pexpect.TIMEOUT, "%",])
    assert i != 0, "Time-Out.... exiting"
    p.sendline("cd ~/install")

Here is the output:

Spawning Expect
Sending cd command
Time-Out.... exiting


How could I be screwing something so simple up??