import urllib

def dict_to_str(d):
    '''Return a str containing each key and value in dict d. Keys and
    values are separated by a space. Each key-value pair is separated by a
    comma.'''
    
    pass
        
def dict_to_str_sorted(d):
    '''Return a str containing each key and value in dict d. Keys and
    values are separated by a space. Each key-value pair is separated by a
    comma, and the pairs are sorted in ascending order by key.'''
    
    pass

def file_to_dict(f):
    '''f is an open file f that contains exchange rate changes as
    floating point numbers separated by whitespace. Return a dict
    of how many times each rate change occurred, with exchange rates as
    keys and the number of occurrences of the exchange rates as int values.'''
    
    pass

def count_data(d):
    '''Given a dict d where the keys are exchange rate changes and values are
    the number of occurrences of each exchange rate change, return the total
    number of exchange rate changes (including duplicates) as an int.'''
    
    pass

def most_common_rate_change(d):
    '''Given a dictionary d where keys are exchange rate changes and values
    are the number of occurrences of each exchange rate, return a list of the
    exchange rate changes that occur the most frequently.'''
    
    pass
    
if __name__ == '__main__':
    
    filename = "http://www.stat.duke.edu/~mw/data-sets/ts_data/exchange-rates"