<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def citation_count(papers, key='ayjid', verbose=False):
 """ Generates citation counts for all of the papers cited by papers. Parameters papers : list A list of :class:`.Paper` instances. key : str Property to use as node key. Default is 'ayjid' (recommended). verbose : bool If True, prints status messages. Returns ------- counts : dict Citation counts for all papers cited by papers. """


    if verbose:
        print "Generating citation counts for "+unicode(len(papers))+" papers..."

    counts = Counter()
    for P in papers:
        if P['citations'] is not None:
            for p in P['citations']:
                counts[p[key]] += 1

    return counts