(f, n, K)
Efficiently multiply ``f`` by ``x**n`` in ``K[x]``.

    Examples
    ========

    >>> from sympy.polys import ring, ZZ
    >>> R, x = ring("x", ZZ)

    >>> R.dup_lshift(x**2 + 1, 2)
    x**4 + x**2
Efficiently multiply ``f`` by ``x**n`` in ``K[x]``.
Efficiently multiply f by x ** n in K [ x ] .
def dup_lshift(f, n, K):
    """
    Efficiently multiply ``f`` by ``x**n`` in ``K[x]``.

    Examples
    ========

    >>> from sympy.polys import ring, ZZ
    >>> R, x = ring("x", ZZ)

    >>> R.dup_lshift(x**2 + 1, 2)
    x**4 + x**2

    """
    if not f:
        return f
    else:
        return f + [K.zero]*n
def dup_lshift ( f , n , K ) : if not f : return f else : return f + [ K . zero ] * n