Mutable defaults in function/method definitions

[mguaypaq]

Several functions and methods in Sage have mutable default arguments, especially lists. This is generally frowned upon, at least on the Python side (see http://effbot.org/zone/default-values.htm), since it can cause so many subtle bugs, and there's usually no benefit to doing this instead of using a tuple or None (with creation of the mutable argument in the function body).

Are there any objections to fixing this?

Here is a somewhat filtered (and certainly non-exhaustive) output of a naive grep search through the codebase:

sage/combinat/partition.py:    def content(self, r, c, multicharge=[0]):
sage/combinat/partition.py:    def dimension(self, smaller = [], k = 1):
sage/combinat/root_system/pieri_factors.py:    def __classcall__(cls, W, min_length = 0, max_length = infinity, min_support = frozenset([]), max_support = None):
sage/combinat/root_system/weight_lattice_realizations.py:        def plot(self, size=[[0],[0]], projection='usual', simple_roots=True, fundamental_weights=True, alcovewalks=[]):
sage/combinat/tableau.py:    def content(self, k, multicharge=[0]):
sage/combinat/designs/covering_design.py:    def __init__(self, v=0, k=0, t=0, size=0, points=[], blocks=[], low_bd=0, method='', creator ='',timestamp=''):
sage/combinat/integer_vector.py:def _slider01(A, t, k, p1, p2, fixedcols=[]):
sage/plot/graphics.py:    def _extract_kwds_for_show(cls, kwds, ignore=[]):
sage/matrix/benchmark.py:def report(F, title, systems = ['sage', 'magma'], **kwds):
sage/server/notebook/worksheet.py:    def do_sage_extensions_preparsing(self, s, files_seen_so_far=[], this_file=''):
sage/sets/family.py:def Family(indices, function = None, hidden_keys = [], hidden_function = None, lazy = False, name=None):
sage/modular/etaproducts.py:def eta_poly_relations(eta_elements, degree, labels=['x1','x2'], verbose=False):
sage/modular/modform/find_generators.py:    def generators(self, maxweight=8, prec=10, start_gens=[], start_weight=2):
sage/modular/modform/find_generators.py:    def gen_forms(self, maxweight=8, start_gens=[], start_weight=2):
sage/quadratic_forms/random_quadraticform.py:def random_quadraticform(R, n, rand_arg_list=[]):
sage/quadratic_forms/random_quadraticform.py:def random_quadraticform_with_conditions(R, n, condition_list=[], rand_arg_list=[]):
sage/groups/perm_gps/cubegroup.py:def color_of_square(facet, colors=['lpurple', 'yellow', 'red', 'green', 'orange', 'blue']):
sage/groups/perm_gps/cubegroup.py:    def plot_cube(self, mv, title=True, colors = [lpurple, yellow, red, green, orange, blue]):
sage/groups/perm_gps/cubegroup.py:    def __init__(self, state=None, history=[], colors=[lpurple,yellow,red,green,orange,blue]):
sage/rings/number_field/totallyreal_rel.py:def enumerate_totallyreal_fields_rel(F, m, B, a = [], verbose=0, return_seqs=False):
sage/rings/number_field/number_field_ideal.py:    def invertible_residues_mod(self, subgp_gens=[], reduce=True):
sage/rings/polynomial/groebner_fan.py:    def __init__(self, gfan_polyhedral_fan, parameter_indices = []):
sage/rings/polynomial/groebner_fan.py:    def __init__(self, gfan_polyhedral_fan, polynomial_system, poly_ring, parameters = []):
sage/rings/polynomial/groebner_fan.py:    def tropical_intersection(self, parameters = [], symmetry_generators = [], *args, **kwds):
sage/geometry/polytope.py:    def convex_hull(self, points=[]):
sage/doctest/forker.py:    def __init__(self, source, options, funclist=[]):
sage/homology/cubical_complex.py:    def __init__(self, maximal_faces=[], **kwds):
sage/interfaces/magma.py:    def function_call(self, function, args=[], params={}, nvals=1):
sage/interfaces/qepcad.py:    def __init__(self, formula, vars, qvars=[]):
sage/interfaces/frobby.py:    def __call__(self, action, input=None, options=[], verbose=False):
sage/misc/preparser.py:def containing_block(code, ix, delimiters=['()','[]','{}'], require_delim=True):
sage/misc/sage_unittest.py:    def run(self, category = None, skip = [], catch = True, raise_on_failure = False, **options):
sage/misc/latex.py:    def __init__(self, bb=False, delimiters=["(", ")"]):
sage/misc/profiler.py:    def __init__(self, systems=[], verbose=False):
sage/schemes/elliptic_curves/ell_egros.py:def is_possible_j(j,S=[]):
sage/schemes/elliptic_curves/ell_egros.py:def egros_from_j_1728(S=[]): 
sage/schemes/elliptic_curves/ell_egros.py:def egros_from_j_0(S=[]):
sage/schemes/elliptic_curves/ell_egros.py:def egros_from_j(j,S=[]): 
sage/schemes/elliptic_curves/ell_egros.py:def egros_from_jlist(jlist,S=[]): 
sage/schemes/elliptic_curves/ell_egros.py:def egros_get_j(S=[], proof=None, verbose=False):
sage/schemes/elliptic_curves/constructor.py:def EllipticCurves_with_good_reduction_outside_S(S=[], proof=None, verbose=False):
sage/schemes/elliptic_curves/ell_number_field.py:    def regulator_of_points(self, points=[], precision=None):
sage/schemes/elliptic_curves/ell_rational_field.py:    def has_good_reduction_outside_S(self,S=[]):

CC: @fchapoton

Component: misc

Issue created by migration from https://trac.sagemath.org/ticket/14795

[mkoeppe]

Changed author from Mathieu Guay-Paquet to none

[mkoeppe]

comment:4

git grep 'def.*=[[]' reveals that we still have many of these as of 9.7.rc2