#!/usr/bin/env python
# encoding: utf-8

from .explicable import Explicable
from .expression import Expression
from .step import Step
from .renderable import Renderable
from .operator import op
from .generic import spe_zip, isNumber, transpose_fill, flatten_list, isPolynom, postfix_op
from functools import wraps


def power_cache(fun):
    """Decorator which cache calculated powers of polynoms """
    cache = {}

    @wraps(fun)
    def cached_fun(self, power):
        if (tuple(self._coef), power) in cache.keys():
            return cache[(tuple(self._coef), power)]
        else:
            poly_powered = fun(self, power)
            cache[(tuple(self._coef), power)] = poly_powered
            return poly_powered
    return cached_fun


class AbstractPolynom(Explicable):

    """The mathematic definition of a polynom. It will be the parent class of Polynom (classical polynoms) and later of SquareRoot polynoms"""

    def __init__(self, coefs=[1], letter="x", name="P"):
        """Initiate the polynom

        :param coef: coefficients of the polynom (ascending degree sorted)
            3 possibles type of coefficent:
                - a : simple "number". [1,2] designate 1 + 2x
                - [a,b,c]: list of coeficient for same degree. [1,[2,3],4] designate 1 + 2x + 3x + 4x^2
                - a: a Expression. [1, Expression("2+3"), 4] designate 1 + (2+3)x + 4x^2
        :param letter: the string describing the unknown
        :param name: Name of the polynom

        >>> P = AbstractPolynom([1, 2, 3])
        >>> P.mainOp
        +
        >>> P.name
        'P'
        >>> P._letter
        'x'
        >>> AbstractPolynom([1]).mainOp
        *
        >>> AbstractPolynom([0, 0, 3]).mainOp
        *
        >>> AbstractPolynom([1, 2, 3])._letter
        'x'
        >>> AbstractPolynom([1, 2, 3], "y")._letter
        'y'
        >>> AbstractPolynom([1, 2, 3], name = "Q").name
        'Q'
        """
        try:
            # Remove 0 at the end of the coefs
            while coefs[-1] == 0:
                coefs = coefs[:-1]
        except IndexError:
            pass

        if coefs == []:
            coefs = [0]

        self.feed_coef(coefs)
        self._letter = letter
        self.name = name

        if self.is_monom():
            self.mainOp = op.mul
        else:
            self.mainOp = op.add

        self._isPolynom = 1
        
        pstf_tokens = self.compute_postfix_tokens()
        super(AbstractPolynom, self).__init__(pstf_tokens)

    def feed_coef(self, l_coef):
        """Feed coef of the polynom. Manage differently whether it's a number or an expression

        :l_coef: list of coef
        """
        self._coef = []
        for coef in l_coef:
            if isinstance(coef, list) and len(coef) == 1:
                self._coef.append(coef[0])
            else:
                self._coef.append(coef)

    @property
    def degree(self):
        """Getting the degree fo the polynom

        :returns: the degree of the polynom

        >>> AbstractPolynom([1, 2, 3]).degree
        2
        >>> AbstractPolynom([1]).degree
        0
        """
        return len(self._coef) - 1

    def is_monom(self):
        """is the polynom a monom (only one coefficent)

        :returns: 1 if yes 0 otherwise

        >>> AbstractPolynom([1, 2, 3]).is_monom()
        0
        >>> AbstractPolynom([1]).is_monom()
        1
        """
        if len([i for i in self._coef if i != 0]) == 1:
            return 1
        else:
            return 0

    def give_name(self, name):
        self.name = name

    def __str__(self):
        return str(Expression(self.postfix_tokens))

    def __repr__(self):
        return  "< {cls} {letter} {coefs}>".format(
                cls = str(self.__class__).split('.')[-1][:-2],
                letter = str(self._letter),
                coefs = str(self._coef))

    def coef_postfix(self, a, i):
        """Return the postfix display of a coeficient

        :param a: value for the coeficient (/!\ as a postfix list)
        :param i: power
        :returns: postfix tokens of coef

        >>> p = AbstractPolynom()
        >>> p.coef_postfix([3],2)
        [3, 'x', 2, ^, *]
        >>> p.coef_postfix([0],1)
        []
        >>> p.coef_postfix([3],0)
        [3]
        >>> p.coef_postfix([3],1)
        [3, 'x', *]
        >>> p.coef_postfix([1],1)
        ['x']
        >>> p.coef_postfix([1],2)
        ['x', 2, ^]

        """
        if a == [0]:
            ans = []
        elif i == 0:
            ans = a
        elif i == 1:
            ans = a * (a not in [[1], [-1]]) + \
                    [self._letter] + \
                    [op.mul] * (a not in [[1], [-1]]) + \
                    [op.sub1] * (a == [-1])
        else:
            ans = a * (a not in [[1], [-1]]) + \
                    [self._letter, i, op.pw] + \
                    [op.mul] * (a not in [[1], [-1]]) + \
                    [op.sub1] * (a == [-1])

        return ans

    def coefs_postifx(self):
        """ Return list of postfix coef with the the right power letter

        >>> p = AbstractPolynom([1, 2])
        >>> p.coefs_postifx()
        [[1], [2, 'x', *]]
        >>> p = AbstractPolynom([1, -2])
        >>> p.coefs_postifx()
        [[1], [-2, 'x', *]]
        >>> p = AbstractPolynom([1,2,3])
        >>> p.coefs_postifx()
        [[1], [2, 'x', *], [3, 'x', 2, ^, *]]
        >>> p = AbstractPolynom([1])
        >>> p.coefs_postifx()
        [[1]]
        >>> p = AbstractPolynom([0])
        >>> p.coefs_postifx()
        [[0]]
        >>> p = AbstractPolynom([0, 1, 1, 0])
        >>> p.coefs_postifx()
        [['x'], ['x', 2, ^]]
        >>> p = AbstractPolynom([1,[2,3]])
        >>> p.coefs_postifx()
        [[1], [3, 'x', *], [2, 'x', *]]
        >>> p = AbstractPolynom([1,[2,-3]])
        >>> p.coefs_postifx()
        [[1], [-3, 'x', *], [2, 'x', *]]
        >>> p = AbstractPolynom([1,[-2,-3]])
        >>> p.coefs_postifx()
        [[1], [-3, 'x', *], [-2, 'x', *]]
        >>> p = AbstractPolynom([1,[-2,0]])
        >>> p.coefs_postifx()
        [[1], [-2, 'x', *]]
        >>> from mapytex.calculus.expression import Expression
        >>> from mapytex.calculus.operator import op
        >>> e = Expression([2,3,op.add])
        >>> p = AbstractPolynom([1,e])
        >>> p.coefs_postifx()
        [[1], [2, 3, +, 'x', *]]
        """
        if not [i for i in self._coef if i!= 0]:
            return [[0]]

        raw_coefs = []
        for (pw, coef) in enumerate(self._coef):
            if isinstance(coef, list):
                for c in coef[::-1]:
                    try:
                        raw_coefs.append(self.coef_postfix(c.postfix_tokens, pw))
                    except AttributeError:
                        raw_coefs.append(self.coef_postfix([c], pw))
            elif coef != 0:
                try:
                    raw_coefs.append(self.coef_postfix(coef.postfix_tokens, pw))
                except AttributeError:
                    raw_coefs.append(self.coef_postfix([coef], pw))


        return [i for i in raw_coefs if i != []]

    def compute_postfix_tokens(self):
        """Return the postfix form of the polynom

        :returns: the postfix list of polynom's tokens

        >>> p = AbstractPolynom([1, 2])
        >>> p.postfix_tokens
        [2, 'x', *, 1, +]
        >>> p = AbstractPolynom([1, -2])
        >>> p.postfix_tokens
        [-2, 'x', *, 1, +]
        >>> p = AbstractPolynom([1,2,3])
        >>> p.postfix_tokens
        [3, 'x', 2, ^, *, 2, 'x', *, +, 1, +]
        >>> p = AbstractPolynom([1])
        >>> p.postfix_tokens
        [1]
        >>> p = AbstractPolynom([0])
        >>> p.postfix_tokens
        [0]
        >>> p = AbstractPolynom([1,[2,3]])
        >>> p.postfix_tokens
        [2, 'x', *, 3, 'x', *, +, 1, +]
        >>> p = AbstractPolynom([1,[2,-3]])
        >>> p.postfix_tokens
        [2, 'x', *, -3, 'x', *, +, 1, +]
        >>> p = AbstractPolynom([1,[-2,-3]])
        >>> p.postfix_tokens
        [-2, 'x', *, -3, 'x', *, +, 1, +]
        >>> from mapytex.calculus.expression import Expression
        >>> from mapytex.calculus.operator import op
        >>> e = Expression([2,3,op.add])
        >>> p = AbstractPolynom([1,e])
        >>> p.postfix_tokens
        [2, 3, +, 'x', *, 1, +]

        """
        raw_coefs = self.coefs_postifx()

        pstfx =  postfix_op(raw_coefs[::-1], op.add)
        return flatten_list(pstfx)

    def conv2poly(self, other):
        """Convert anything number into a polynom

        >>> P = AbstractPolynom([1,2,3])
        >>> P.conv2poly(1)
        < AbstractPolynom x [1]>
        >>> P.conv2poly(0)
        < AbstractPolynom x [0]>
        >>> Q = AbstractPolynom([3, 2, 1], 'x')
        >>> P.conv2poly(Q)
        < AbstractPolynom x [3, 2, 1]>
        >>> Q = AbstractPolynom([3, 2, 1], 'y')
        >>> P.conv2poly(Q)
        < AbstractPolynom x [< AbstractPolynom y [3, 2, 1]>]>
        """
        if (isNumber(other) and not isPolynom(other)) or \
            (isPolynom(other) and self._letter != other._letter):
                #ans = self.__class__([other], letter=self._letter)
                ans = AbstractPolynom([other], letter=self._letter)
                ans.steal_history(other)
                return ans
        elif isPolynom(other):
            return other
        else:
            raise ValueError(
                    type(other) +
                    " can't be converted into a polynom"
                    )

    def reduce(self):
        """Compute coefficients which have same degree

        :returns: new AbstractPolynom with numbers coefficients

        >>> P = AbstractPolynom([1,2,3])
        >>> Q = P.reduce()
        >>> Q
        < AbstractPolynom x [1, 2, 3]>
        >>> Q.steps
        [< Step [3, 'x', 2, ^, *, 2, 'x', *, +, 1, +]>, < Step [3, 'x', 2, ^, *, 2, 'x', *, +, 1, +]>]
        >>> P = AbstractPolynom([[1,2], [3,4,5], 6])
        >>> Q = P.reduce()
        >>> Q
        < AbstractPolynom x [3, 12, 6]>
        >>> for i in Q.explain():
        ...     print(i)
        6 x^{  2 } + 3 x + 4 x + 5 x + 1 + 2
        6 x^{  2 } + ( 3 + 4 + 5 ) x + 1 + 2
        6 x^{  2 } + ( 7 + 5 ) x + 3
        6 x^{  2 } + 12 x + 3
        >>> Q.steps
        [< Step [6, 'x', 2, ^, *, 3, 'x', *, +, 4, 'x', *, +, 5, 'x', *, +, 1, +, 2, +]>, < Step [6, 'x', 2, ^, *, 3, 4, +, 5, +, 'x', *, +, 1, 2, +, +]>, < Step [6, 'x', 2, ^, *, 7, 5, +, 'x', *, +, 3, +]>, < Step [6, 'x', 2, ^, *, 12, 'x', *, +, 3, +]>]
        >>> P = AbstractPolynom([[1,2], [3,4,5], 6], 'y')
        >>> Q = P.reduce()
        >>> Q
        < AbstractPolynom y [3, 12, 6]>
        >>> for i in Q.explain():
        ...     print(i)
        6 y^{  2 } + 3 y + 4 y + 5 y + 1 + 2
        6 y^{  2 } + ( 3 + 4 + 5 ) y + 1 + 2
        6 y^{  2 } + ( 7 + 5 ) y + 3
        6 y^{  2 } + 12 y + 3
        >>> P = AbstractPolynom([1,2])
        >>> Q = AbstractPolynom([P,3], 'y')
        >>> Q
        < AbstractPolynom y [< AbstractPolynom x [1, 2]>, 3]>
        >>> Q = Q.reduce()
        >>> for i in Q.explain():
        ...    print(i)
        3 y + 2 x + 1
        >>> P = AbstractPolynom([1,2])
        >>> Q = AbstractPolynom([[P,1],3], 'y')
        >>> Q
        < AbstractPolynom y [[< AbstractPolynom x [1, 2]>, 1], 3]>
        >>> Q = Q.reduce()
        >>> for i in Q.explain():
        ...    print(i)
        3 y + 2 x + 1 + 1
        3 y + 2 x + 2
        """
        smpl_coef = []
        for coef in self._coef:

            if isinstance(coef, list):
                coef_exp = AbstractPolynom.smpl_coef_list(coef)

            else:
                try:
                    coef_exp = coef.simplify()
                except AttributeError:
                    coef_exp = coef

            smpl_coef.append(coef_exp)

        ans = AbstractPolynom(smpl_coef, self._letter)

        ini_step = [Step(self)]
        for s in Explicable.merge_history(smpl_coef):
            ini_step.append(Step(AbstractPolynom(s, self._letter)))

        ans.this_append_before(
                ini_step
                #AbstractPolynom(s)
                #for s in Expression.develop_steps(smpl_coef)
                )

        return ans

    def simplify(self):
        """Same as reduce """
        if isNumber(self._letter):
            return self.replace_letter(self._letter).simplify()
        return self.reduce()

    @classmethod
    def smpl_coef_list(cls,  coef_list):
        """ Simplify the coef when it is a list

        :param coef_list: the list discribing the coef
        :returns: the simplify coef

        >>> c = AbstractPolynom.smpl_coef_list([1, 2, 3])
        >>> c
        6
        >>> c.steps
        [< Step [1, 2, +, 3, +]>, < Step [1, 2, +, 3, +]>, < Step [3, 3, +]>, < Step [3, 3, +]>, < Step [6]>]
        >>> c = AbstractPolynom.smpl_coef_list([Expression('2*2'), 3])
        >>> c
        7
        >>> c.steps
        [< Step [2, 2, *, 3, +]>, < Step [4, 3, +]>, < Step [4, 3, +]>, < Step [7]>]
        >>> c = AbstractPolynom.smpl_coef_list([0, 2, 0])
        >>> c
        2
        >>> c.steps
        [< Step [2]>]
        """
        # Simplify each element before adding them
        smpl_elem = []
        for c in coef_list:
            try:
                smpl_c = c.simplify()
            except AttributeError:
                smpl_c = c
            smpl_elem.append(smpl_c)

        pstfx_add = postfix_op(
                [i for i in smpl_elem if i != 0],
                op.add
                )

        steps = Expression.develop_steps(pstfx_add)

        ans = Expression(pstfx_add).simplify()
        ans.this_append_before(steps)
        return ans

    def replace_letter(self, letter):
        r""" Replace the letter in the expression

        :param letter: the new letter.
        :returns: The expression with the new letter.

        >>> A = AbstractPolynom([1, 2])
        >>> A
        < AbstractPolynom x [1, 2]>
        >>> B = A.replace_letter("y")
        >>> B
        < Expression [2, < Polynom y [0, 1]>, *, 1, +]>
        >>> C = A.replace_letter(2)
        >>> C
        < Expression [2, 2, *, 1, +]>
        >>> e = Expression('2+3').simplify()
        >>> D = A.replace_letter(e)
        >>> D
        < Expression [2, 5, *, 1, +]>
        >>> for i in D.explain():
        ...    print(i)
        2 ( 2 + 3 ) + 1
        2 \times 5 + 1

        """
        exp_to_replace = Expression(letter)
        exp_to_replace.steal_history(letter)

        postfix_exp = [
                exp_to_replace if i == self._letter
                else i
                for i in self.postfix_tokens
                ]
        ini_step = Expression.develop_steps(postfix_exp)

        ans = Expression(postfix_exp)
        ans.this_append_before(ini_step)

        return ans

    def __eq__(self, other):
        try:
            o_poly = self.conv2poly(other)
            return self._coef == o_poly._coef
        except TypeError:
            return 0

    def __add__(self, other):
        """ Overload +

        >>> P = AbstractPolynom([1,2,3])
        >>> Q = AbstractPolynom([4,5])
        >>> R = P+Q
        >>> R
        < AbstractPolynom x [5, 7, 3]>
        >>> for i in R.explain():
        ...    print(i)
        3 x^{  2 } + 2 x + 1 + 5 x + 4
        3 x^{  2 } + 2 x + 5 x + 1 + 4
        3 x^{  2 } + ( 2 + 5 ) x + 1 + 4
        3 x^{  2 } + 7 x + 5
        >>> R.steps
        [< Step [3, 'x', 2, ^, *, 2, 'x', *, +, 1, +, 5, 'x', *, 4, +, +]>, < Step [3, 'x', 2, ^, *, 2, 'x', *, +, 5, 'x', *, +, 1, +, 4, +]>, < Step [3, 'x', 2, ^, *, 2, 5, +, 'x', *, +, 1, 4, +, +]>, < Step [3, 'x', 2, ^, *, 7, 'x', *, +, 5, +]>]
        >>> Q = AbstractPolynom([4,5], letter = 'y')
        >>> R = P+Q
        >>> R
        < AbstractPolynom x [< AbstractPolynom y [5, 5]>, 2, 3]>
        >>> for i in R.explain():
        ...    print(i)
        3 x^{  2 } + 2 x + 1 + 5 y + 4
        3 x^{  2 } + 2 x + 5 y + 1 + 4
        3 x^{  2 } + 2 x + 5 y + 5

        """
        o_poly = self.conv2poly(other)

        n_coef = spe_zip(self._coef, o_poly._coef)
        p = AbstractPolynom(n_coef, letter=self._letter)

        ini_step = [Step([self, o_poly, op.add])]

        ans = p.simplify()
        ans.this_append_before(ini_step)
        return ans

    def __radd__(self, other):
        o_poly = self.conv2poly(other)
        return o_poly.__add__(self)

    def __neg__(self):
        """ overload - (as arity 1 operator)

        >>> P = AbstractPolynom([1,2,3])
        >>> Q = -P
        >>> Q
        < AbstractPolynom x [-1, -2, -3]>
        >>> for i in Q.explain():
        ...    print(i)
        - ( 3 x^{  2 } + 2 x + 1 )
        -3 x^{  2 } - 2 x - 1
        >>> Q.steps
        [< Step [3, 'x', 2, ^, *, 2, 'x', *, +, 1, +, -]>, < Step [-3, 'x', 2, ^, *, -2, 'x', *, +, -1, +]>, < Step [-3, 'x', 2, ^, *, -2, 'x', *, +, -1, +]>]
        """
        ini_step = [Step(self.postfix_tokens + [op.sub1])]
        ans = AbstractPolynom([-i for i in self._coef],
                              letter=self._letter).simplify()
        ans.this_append_before(ini_step)
        return ans

    def __sub__(self, other):
        """ overload -

        >>> P = AbstractPolynom([1,2,3])
        >>> Q = AbstractPolynom([4,5,6])
        >>> R = P - Q
        >>> R
        < AbstractPolynom x [-3, -3, -3]>
        >>> for i in R.explain():
        ...     print(i)
        3 x^{  2 } + 2 x + 1 - ( 6 x^{  2 } + 5 x + 4 )
        3 x^{  2 } + 2 x + 1 - 6 x^{  2 } - 5 x - 4
        3 x^{  2 } - 6 x^{  2 } + 2 x - 5 x + 1 - 4
        ( 3 - 6 ) x^{  2 } + ( 2 - 5 ) x + 1 - 4
        -3 x^{  2 } - 3 x - 3
        >>> R.steps
        [< Step [3, 'x', 2, ^, *, 2, 'x', *, +, 1, +, 6, 'x', 2, ^, *, 5, 'x', *, +, 4, +, -]>, < Step [3, 'x', 2, ^, *, 2, 'x', *, +, 1, +, -6, 'x', 2, ^, *, -5, 'x', *, +, -4, +, +]>, < Step [3, 'x', 2, ^, *, -6, 'x', 2, ^, *, +, 2, 'x', *, +, -5, 'x', *, +, 1, +, -4, +]>, < Step [3, -6, +, 'x', 2, ^, *, 2, -5, +, 'x', *, +, 1, -4, +, +]>, < Step [-3, 'x', 2, ^, *, -3, 'x', *, +, -3, +]>]
        """
        o_poly = self.conv2poly(other)
        ini_step = [Step(self.postfix_tokens +
                               o_poly.postfix_tokens + [op.sub])]
        o_poly = -o_poly

        ans = self + o_poly
        ans.this_append_before(ini_step)

        return ans

    def __rsub__(self, other):
        o_poly = self.conv2poly(other)

        return o_poly.__sub__(self)

    def __mul__(self, other):
        r""" Overload *

        >>> p = AbstractPolynom([1,2])
        >>> p*3
        < AbstractPolynom x [3, 6]>
        >>> for i in (p*3).explain():
        ...    print(i)
        ( 2 x + 1 ) \times 3
        2 \times 3 x + 3
        6 x + 3
        >>> (p*3).steps
        [< Step [2, 'x', *, 1, +, 3, *]>, < Step [2, 3, *, 'x', *, 3, +]>, < Step [2, 3, *, 'x', *, 3, +]>, < Step [6, 'x', *, 3, +]>]
        >>> q = AbstractPolynom([0,0,4])
        >>> q*3
        < AbstractPolynom x [0, 0, 12]>
        >>> for i in (q*3).explain():
        ...    print(i)
        4 x^{  2 } \times 3
        4 \times 3 x^{  2 }
        12 x^{  2 }
        >>> (q*3).steps
        [< Step [4, 'x', 2, ^, *, 3, *]>, < Step [4, 3, *, 'x', 2, ^, *]>, < Step [4, 3, *, 'x', 2, ^, *]>, < Step [12, 'x', 2, ^, *]>]
        >>> r = AbstractPolynom([0,1])
        >>> r*3
        < AbstractPolynom x [0, 3]>
        >>> (r*3).steps
        [< Step ['x', 3, *]>, < Step [3, 'x', *]>, < Step [3, 'x', *]>]
        >>> p*q
        < AbstractPolynom x [0, 0, 4, 8]>
        >>> (p*q).steps
        [< Step [2, 'x', *, 1, +, 4, 'x', 2, ^, *, *]>, < Step [2, 4, *, 'x', 3, ^, *, 4, 'x', 2, ^, *, +]>, < Step [2, 4, *, 'x', 3, ^, *, 4, 'x', 2, ^, *, +]>, < Step [8, 'x', 3, ^, *, 4, 'x', 2, ^, *, +]>]
        >>> for i in (p*q).explain():
        ...    print(i)
        ( 2 x + 1 ) \times 4 x^{  2 }
        2 \times 4 x^{  3 } + 4 x^{  2 }
        8 x^{  3 } + 4 x^{  2 }
        >>> p*r
        < AbstractPolynom x [0, 1, 2]>
        >>> P = AbstractPolynom([1,2,3])
        >>> Q = AbstractPolynom([4,5,6])
        >>> P*Q
        < AbstractPolynom x [4, 13, 28, 27, 18]>
        """
        o_poly = self.conv2poly(other)

        coefs = [0] * (self.degree + o_poly.degree + 1)
        for (i, a) in enumerate(self._coef):
            for (j, b) in enumerate(o_poly._coef):
                if a == 0 or b == 0:
                    elem = 0
                elif a == 1:
                    elem = b
                elif b == 1:
                    elem = a
                else:
                    elem = Expression([a, b, op.mul])

                if coefs[i + j] == 0:
                    coefs[i + j] = elem
                elif elem != 0:
                    if isinstance(coefs[i + j], list):
                        coefs[i + j] += [elem]
                    else:
                        coefs[i + j] = [coefs[i + j], elem]

        p = AbstractPolynom(coefs, letter=self._letter)
        ini_step = [Step(self.postfix_tokens +
                               o_poly.postfix_tokens + [op.mul])]
        ans = p.simplify()

        ans.this_append_before(ini_step)
        return ans

    def __rmul__(self, other):
        o_poly = self.conv2poly(other)

        return o_poly.__mul__(self)

    def __truediv__(self, other):
        r""" Overload /

        >>> P = AbstractPolynom([1, 2, 4])
        >>> P / 2
        < AbstractPolynom x [< Fraction 1 / 2>, 1, 2]>
        >>> for i in (P/2).explain():
        ...    print(i)
        \frac{ 4 x^{  2 } + 2 x + 1 }{ 2 }
        \frac{ 4 }{ 2 } x^{  2 } + \frac{ 2 }{ 2 } x + \frac{ 1 }{ 2 }
        2 x^{  2 } + x + \frac{ 1 }{ 2 }


        """
        ans_coefs = [Expression([c, other, op.div]) if c != 0
                else 0
                for c in self._coef
                ]

        ans = AbstractPolynom(ans_coefs, letter=self._letter)
        ini_step = [Step(
            self.postfix_tokens +
            [other, op.div]
            )]

        ans = ans.simplify()
        ans.this_append_before(ini_step)
        return ans

    @power_cache
    def __pow__(self, power):
        r""" Overload **

        >>> p = AbstractPolynom([0,0,3])
        >>> p**2
        < AbstractPolynom x [0, 0, 0, 0, 9]>
        >>> (p**2).steps
        [< Step [3, 'x', 2, ^, *, 2, ^]>, < Step [3, 2, ^, 'x', 4, ^, *]>, < Step [3, 2, ^, 'x', 4, ^, *]>, < Step [9, 'x', 4, ^, *]>]
        >>> for i in (p**2).explain():
        ...    print(i)
        ( 3 x^{  2 } )^{  2 }
        3^{  2 } x^{  4 }
        9 x^{  4 }
        >>> p = AbstractPolynom([1,2])
        >>> p**2
        < AbstractPolynom x [1, 4, 4]>
        >>> (p**2).steps
        [< Step [2, 'x', *, 1, +, 2, ^]>, < Step [2, 'x', *, 1, +, 2, 'x', *, 1, +, *]>, < Step [2, 2, *, 'x', 2, ^, *, 2, 'x', *, +, 2, 'x', *, +, 1, +]>, < Step [2, 2, *, 'x', 2, ^, *, 2, 2, +, 'x', *, +, 1, +]>, < Step [4, 'x', 2, ^, *, 4, 'x', *, +, 1, +]>]
        >>> for i in (p**2).explain():
        ...    print(i)
        ( 2 x + 1 )^{  2 }
        ( 2 x + 1 ) ( 2 x + 1 )
        2 \times 2 x^{  2 } + 2 x + 2 x + 1
        2 \times 2 x^{  2 } + ( 2 + 2 ) x + 1
        4 x^{  2 } + 4 x + 1
        >>> p = AbstractPolynom([0,0,1])
        >>> p**3
        < AbstractPolynom x [0, 0, 0, 0, 0, 0, 1]>
        >>> p = AbstractPolynom([1,2,3])
        >>> p**2
        < AbstractPolynom x [1, 4, 10, 12, 9]>

        """
        if not type(power):
            raise ValueError(
                "Can't raise {obj} to {pw} power".format(
                    obj=self.__class__, pw=str(power)))

        ini_step = [Step(self.postfix_tokens + [power, op.pw])]

        if self.is_monom():
            if self._coef[self.degree] == 1:
                coefs = [0] * self.degree * power + [1]
                p = AbstractPolynom(coefs, letter=self._letter)
                ans = p
            else:
                coefs = [0] * self.degree * power + \
                    [Expression([self._coef[self.degree], power, op.pw])]
                p = AbstractPolynom(coefs, letter=self._letter)
                ans = p.simplify()
        else:
            if power == 2:
                ans = self * self
            else:
                # TODO: faudrait changer ça c'est pas très sérieux |ven. févr.
                # 27 22:08:00 CET 2015
                raise AttributeError(
                    "__pw__ not implemented yet when power is greatter than 2")

        ans.this_append_before(ini_step)
        return ans

    def __xor__(self, power):
        return self.__pow__(power)

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