def __init__(self, coefficient, **kwargs):
    self.letteralPart = dict()
    for unknown in kwargs:
        # Doesn't include in the dictionary the unknowns with
        # degree < = 0
        if kwargs[unknown] > 0:
            self.letteralPart[unknown] = kwargs[unknown]

    # Calculates the degree of the monomial
    self.degree = 0
    for unknownDegree in self.letteralPart.values():
        self.degree += unknownDegree

class Monomial:
    """A class which provides some methods to manage monomials"""

    def __init__(self, coefficient, *args, **kwargs):
        """Build a list which has for first element the
        coefficient of the monomial and for second a dictionary
        that has for keys the unknown quantities and for values
        the grade of the unknown quantities.
        Example:
          >>> myMonomial = Monomial(3, x=1, y=3)
          >>> print myMonomial.structure()
          [3, {'x': 1, 'y': 2}]
          >>> print myMonomial
          3xy^2
         """
        self.letteralPart = {}
        self.coefficient = Rational(coefficient)
        self.monomial = [self.coefficient, self.letteralPart]
        for unknown in kwargs.items():
            ## unknown[0] -> letter of the unknown quantity
            ## unknown[1] -> grade of the unknown quantity
            self.letteralPart[unknown[0]] = unknown[1]