fix some docstring. small fix.

src/sage/modular/quasimodform/element.py

@@ -35,7 +35,8 @@ class QuasiModularFormsElement(ModuleElement):
 
         f_0 + f_1 E_2 + f_2 E_2^2 + \cdots + f_m E_2^m
 
-    where each `f_i` a graded modular form element (see :meth:``)
+    where each `f_i` a graded modular form element
+    (see :class:`~sage.modular.modform.element.GradedModularFormElement`)
 
     EXAMPLES::
 
@@ -53,9 +54,11 @@ class QuasiModularFormsElement(ModuleElement):
         sage: QM.0 == QM.1
         False
 
-    Quasimodular forms ring element can be created via a polynomial in `E2`::
+    Quasimodular forms ring element can be created via a polynomial in `E2` over the ring of modular forms::
 
         sage: E2 = QM.polygen()
+        sage: E2.parent()
+        Univariate Polynomial Ring in E2 over Ring of Modular Forms for Modular Group SL(2,Z) over Rational Field
         sage: QM(E2)
         1 - 24*q - 72*q^2 - 96*q^3 - 168*q^4 - 144*q^5 + O(q^6)
         sage: M = QM.modular_forms_subring()

src/sage/modular/quasimodform/ring.py

@@ -46,8 +46,9 @@
 
 .. NOTE:
 
-    Only the ring of quasimodular forms for the full modular group have been
+    - Only the ring of quasimodular forms for the full modular group have been
     implemented.
+    - Currently, the only supported base ring is the Rational Field.
 
 AUTHORS:
 
@@ -99,6 +100,17 @@ class QuasiModularForms(Parent, UniqueRepresentation):
 
         sage: QM.weigt_2_eisenstein_series()
         1 - 24*q - 72*q^2 - 96*q^3 - 168*q^4 - 144*q^5 + O(q^6)
+
+    The current implementation of quasimodular forms is only for the full modular group and for the ring of rationnal numbers::
+
+        sage: QuasiModularForms(Gamma0(2))
+        Traceback (most recent call last):
+        ...
+        NotImplementedError: space of quasimodular forms are only implemented for the full modular group
+        sage: QuasiModularForms(1, GF(5))
+        Traceback (most recent call last):
+        ...
+        NotImplementedError: base ring other than Q are not yet supported for quasimodular forms ring
     """
     Element = QuasiModularFormsElement
     def __init__(self, group=1, base_ring=QQ, name='E2'):
@@ -151,12 +163,11 @@ def __init__(self, group=1, base_ring=QQ, name='E2'):
         elif not is_CongruenceSubgroup(group):
             raise ValueError("Group (=%s) should be a congruence subgroup" % group)
         elif group is not Gamma0(1):
-            raise NotImplementedError("space of quasimodular forms are implemented for the full modular group")
+            raise NotImplementedError("space of quasimodular forms are only implemented for the full modular group")
 
-        #Check if the base ring is a field
-        #For some reasons, there is a problem when computing a basis of ModularForms
-        if not base_ring.is_field():
-            raise ValueError("The base ring must be a field")
+        #Check if the base ring is the rationnal field
+        if not base_ring != QQ:
+            raise NotImplementedError("base ring other than Q are not yet supported for quasimodular forms ring")
 
         self.__group = group
         self.__base_ring = base_ring
@@ -457,41 +468,3 @@ def polygen(self):
             Univariate Polynomial Ring in E2 over Ring of Modular Forms for Modular Group SL(2,Z) over Rational Field
         """
         return self.__polynomial_subring.gen()
-
-    def differentiation_operator(self, f):
-        r"""
-        Compute the formal derivative `q\frac{d}{dq}` of the q-expansion of a
-        quasimodular form `f`
-
-        INPUT:
-
-        - ``f`` -- a power serie in corresponding to the q-expansion of a
-          quasimodular form.
-
-        OUTPUT:
-
-        The power series `q\frac{d}{dq}(f)`
-
-        EXAMPLES::
-
-            sage: M = QuasiModularForms()
-            sage: D = M.differentiation_operator
-            sage: B = M.gens()
-            sage: P = B[0]; Q = B[1]; R = B[2]
-            sage: D(P)
-            -24*q - 144*q^2 - 288*q^3 - 672*q^4 - 720*q^5 + O(q^6)
-            sage: (P.q_expansion()^2 - Q.q_expansion())/12
-            -24*q - 144*q^2 - 288*q^3 - 672*q^4 - 720*q^5 + O(q^6)
-            sage: D(Q)
-            240*q + 4320*q^2 + 20160*q^3 + 70080*q^4 + 151200*q^5 + O(q^6)
-            sage: (P.q_expansion()*Q.q_expansion() - R.q_expansion())/3
-            240*q + 4320*q^2 + 20160*q^3 + 70080*q^4 + 151200*q^5 + O(q^6)
-            sage: D(R)
-            -504*q - 33264*q^2 - 368928*q^3 - 2130912*q^4 - 7877520*q^5 + O(q^6)
-            sage: (P.q_expansion()*R.q_expansion() - Q.q_expansion()^2)/2
-            -504*q - 33264*q^2 - 368928*q^3 - 2130912*q^4 - 7877520*q^5 + O(q^6)
-
-        TODO:: This method need some work. It should return a QuasiModularFormsElement (not a power series in q)
-        """
-        q = f.q_expansion().parent().gen()
-        return q*f.q_expansion().derivative()