While loops for a Python noob
<p>I'm trying to teach my son how to program &amp; I gave him a challenge that I can't do myself.</p>

<p>He has to prompt the user to enter A, B, or C.  Depending on their choice, he'll print some results &amp; other stuff.   While we got this working, I'm trying to do some error handling &amp; check for cases where the input is not A, B, or C.   The code is listed below.  I certainly appreciate any guidance you can offer.</p>

<pre><code>print "************************************************************"
print "*                                                          *"
print "*            Welcome to the cinemas                        *"
print "*                                                          *"
print "************************************************************"
print "*                                                          *"
print "*  What movie would you like to see ?                      *"
print "*                                                          *"
print "*  A) Star Wars                                            *"
print "*  B) Bourne Identity                                      *"
print "*  C) The Hunger Games                                     *"
print "*                                                          *"
print "************************************************************"
movie=raw_input()
while(movie!="A","B","C"):
    print "************************************************************"
    print "*                                                          *"
    print "*            Welcome to the cinemas                        *"
    print "*                                                          *"
    print "************************************************************"
    print "*                                                          *"
    print "*  What movie would you like to see ?                      *"
    print "*                                                          *"
    print "*  A) Star Wars                                            *"
    print "*  B) Bourne Identity                                      *"
    print "*  C) The Hunger Games                                     *"
    print "*                                                          *"
    print "************************************************************"
    movie=raw_input()

print "************************************************************"
print "*                                                          *"
print "*  How many tickets would you like ?                       *"
print "*                                                          *"
print "************************************************************"
quantity =input()
cost = 7.5
if movie =="A":
    print "You are seeing Star Wars"
    price = cost*quantity
    print "You owe ", price
elif movie =="B":
    print "You are seeing Bourne Identity"
    price = cost*quantity
    print "You owe ", price
elif movie =="C":
    print "You are seeing The Hunger Games"
    price = cost*quantity
    print "You owe ", price 
</code></pre>
