import os.path

def get_file():
    '''Prompt for the name of an existing file, open the file for reading,
    and return the file object.  As long as the user enters the name
    of a file that does not exist, print "File does not exist.", and
    prompt them for another name. ''' 

    # Note: os.path.exists(filename) returns True if filename exists,
    # and False, otherwise
    

def get_line(myfile):
    '''Read a line from open file myfile and return it, but with
       the new line character at the end of the line removed and
       all the characters in lower case.'''

def create_dicts(pfile):
    '''Read in the data from the open picture data file, pfile, and
       return a tuple (pictures,faces,places,events), where the file
       format is as described in the assignment handout, and pictures,
       faces, places, and events are the data structures described in
       the assignment handout.'''

    # You definitely want to write a helper function, which you
    # call three times, once for each of the dictionaries faces,
    # places, events.  This will save you lots of typing, and make
    # your code more readable.  

    # Start by initializing pictures, faces, places, and events

    # Then, use a while loop to read lines from the files.  You do
    # not want to use a for-loop, because you want to do different
    # things, depending on where you are in the file.  For example,
    # when you have just read 'faces','events', or 'places' from the
    # file, you want to use a nested loop to read all of the faces,
    # etc. inside that section, stopping when you hit 'end'. 

    # Hint: it would be helpful to define a variable, new_picture,
    # which is True whenever the line that was just read is the
    # name of a new picture, and False otherwise.  You can test new_picture
    # to know when you should add a line to the list of pictures. 

    # Here is the beginning of the while loop:
    line = get_line(pfile)
    while line != "":

    # inside the while loop, test what the current line is, and do
    # something appropriate
    #
    # This will take some thought, trying different things out, etc.
    # 
    # Don't wait until the last minute!


if __name__ == '__main__':
    # first time, use the file a3pdata1.txt
    pfile = get_file()
    (pictures,faces,places,events) = create_dicts(pfile)
    # now, print each of pictures, faces, places, and events in turn
    # see the sample output for the format
    # note that the dictionary entries are printed out in alphabetical
    # order of keys; your program should do that too.
    # Note:  if ks is the list of keys of your dictionary, then
    #        ks.sort() sorts them for you.
    # Note: if you write a function to print a dictionary, it will
    #       save you lots of typing.

    # second time, use the file a3pdata2.txt
    pfile = get_file()
    (pictures,faces,places,events) = create_dicts(pfile)
    # again, print each of pictures, faces, places, and events in turn