Change the generate default type in gp to pset.ret.

This fixes a problem when a STGP user would forget
to set the type_ argument, the generate function
would request primitive of the type 'object'. The
type_ argument is only to accomodate GP mutations.
It is from now on set to None by default, and
replace by pset.ret if the no other type has been
specified.

--HG--
branch : dev

deap/gp.py

@@ -487,7 +487,7 @@ def compileADF(expr, psets):
 ######################################
 # GP Program generation functions    #
 ######################################
-def genFull(pset, min_, max_, type_=__type__):
+def genFull(pset, min_, max_, type_=None):
     """Generate an expression where each leaf has a the same depth
     between *min* and *max*.
 
@@ -503,7 +503,7 @@ def condition(height, depth):
         return depth == height
     return generate(pset, min_, max_, condition, type_)
 
-def genGrow(pset, min_, max_, type_=__type__):
+def genGrow(pset, min_, max_, type_=None):
     """Generate an expression where each leaf might have a different depth
     between *min* and *max*.
 
@@ -522,7 +522,7 @@ def condition(height, depth):
                (depth >= min_ and random.random() < pset.terminalRatio)
     return generate(pset, min_, max_, condition, type_)
 
-def genHalfAndHalf(pset, min_, max_, type_=__type__):
+def genHalfAndHalf(pset, min_, max_, type_=None):
     """Generate an expression with a PrimitiveSet *pset*.
     Half the time, the expression is generated with :func:`~deap.gp.genGrow`,
     the other half, the expression is generated with :func:`~deap.gp.genFull`.
@@ -537,7 +537,7 @@ def genHalfAndHalf(pset, min_, max_, type_=__type__):
     method = random.choice((genGrow, genFull))
     return method(pset, min_, max_, type_)
 
-def genRamped(pset, min_, max_, type_=__type__):
+def genRamped(pset, min_, max_, type_=None):
     """
     .. deprecated:: 1.0
         The function has been renamed. Use :func:`~deap.gp.genHalfAndHalf` instead.
@@ -546,7 +546,7 @@ def genRamped(pset, min_, max_, type_=__type__):
                   FutureWarning)
     return genHalfAndHalf(pset, min_, max_, type_)
 
-def generate(pset, min_, max_, condition, type_=__type__):
+def generate(pset, min_, max_, condition, type_=None):
     """Generate a Tree as a list of list. The tree is build
     from the root to the leaves, and it stop growing when the
     condition is fulfilled.
@@ -562,6 +562,8 @@ def generate(pset, min_, max_, condition, type_=__type__):
     :returns: A grown tree with leaves at possibly different depths
               dependending on the condition function.
     """
+    if type_ is None:
+        type_ = pset.ret
     expr = []
     height = random.randint(min_, max_)
     stack = [(0, type_)]

examples/gp/spambase.py

@@ -71,7 +71,7 @@ def if_then_else(input, output1, output2):
 creator.create("Individual", gp.PrimitiveTree, fitness=creator.FitnessMax)
 
 toolbox = base.Toolbox()
-toolbox.register("expr", gp.genHalfAndHalf, pset=pset, type_=pset.ret, min_=1, max_=2)
+toolbox.register("expr", gp.genHalfAndHalf, pset=pset, min_=1, max_=2)
 toolbox.register("individual", tools.initIterate, creator.Individual, toolbox.expr)
 toolbox.register("population", tools.initRepeat, list, toolbox.individual)
 toolbox.register("compile", gp.compile, pset=pset)