gh-41089: various small things about len
    
about not using "if len(what):"

plus  a few other minor things

### 📝 Checklist

- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
    
URL: #41089
Reported by: Frédéric Chapoton
Reviewer(s): David Coudert

Author: Release Manager

src/sage/calculus/calculus.py

@@ -2508,7 +2508,7 @@ def symbolic_expression_from_maxima_string(x, equals_sub=False, maxima=maxima):
     maxima.set('_tmp_', x)
 
     # This is inefficient since it so rarely is needed:
-    #r = maxima._eval_line('listofvars(_tmp_);')[1:-1]
+    # r = maxima._eval_line('listofvars(_tmp_);')[1:-1]
 
     s = maxima._eval_line('_tmp_;')
 
@@ -2520,10 +2520,10 @@ def symbolic_expression_from_maxima_string(x, equals_sub=False, maxima=maxima):
     # there is a potential very subtle bug if 'foo is in a string
     # literal -- but string literals should *never* ever be part of a
     # symbolic expression.
-    s = s.replace("'","")
+    s = s.replace("'", "")
 
     delayed_functions = maxima_qp.findall(s)
-    if len(delayed_functions):
+    if delayed_functions:
         for X in delayed_functions:
             if X == '?%at':  # we will replace Maxima's "at" with symbolic evaluation, not a SymbolicFunction
                 pass
@@ -2548,8 +2548,8 @@ def symbolic_expression_from_maxima_string(x, equals_sub=False, maxima=maxima):
     s = s.replace("%","")
 
     s = s.replace("#","!=")  # a lot of this code should be refactored somewhere...
-    #we apply the square-bracket replacing patterns repeatedly
-    #to ensure that nested brackets get handled (from inside to out)
+    # we apply the square-bracket replacing patterns repeatedly
+    # to ensure that nested brackets get handled (from inside to out)
     while True:
         olds = s
         s = polylog_ex.sub('polylog(\\1,', s)

src/sage/coding/codecan/codecan.pyx

@@ -292,7 +292,7 @@ cdef class InnerGroup:
 
             d, _ = self.minimize_by_row_mult(factor * act_col)
             d.pop(first_nz_rep)
-            if len(d):  # there is at least one more multiplication
+            if d:  # there is at least one more multiplication
                 group_changed[0] = True
                 for i in range(self.rank):
                     factor = d.get(self.get_rep(i))

src/sage/data_structures/bounded_integer_sequences.pyx

@@ -1388,7 +1388,7 @@ def _biseq_stresstest():
             L[randint(0, 99)] = L[randint(0, 99)] + L[randint(0, 99)]
         elif branch == 1:
             x = randint(0, 99)
-            if len(L[x]):
+            if L[x]:
                 y = randint(0, len(L[x]) - 1)
                 z = randint(y, len(L[x]) - 1)
                 L[randint(0, 99)] = L[x][y:z]
@@ -1400,7 +1400,7 @@ def _biseq_stresstest():
             t = L[randint(0, 99)].list()
         elif branch == 3:
             x = randint(0, 99)
-            if len(L[x]):
+            if L[x]:
                 y = randint(0, len(L[x])-1)
                 t = L[x][y]
                 try:

src/sage/databases/findstat.py

@@ -2802,7 +2802,7 @@ def __init__(self, id, domain=None, check=True):
         FindStatCombinatorialStatistic.__init__(self)
         Element.__init__(self, FindStatStatistics()) # this is not completely correct, but it works
 
-    def _fetch_first_terms_raw(self):
+    def _fetch_first_terms_raw(self) -> list:
         r"""
         Return the first terms of the compound statistic, as ``(string,
         value)`` pairs, fetched from FindStat.
@@ -2817,7 +2817,7 @@ def _fetch_first_terms_raw(self):
         """
         fields = "Values"
         url = FINDSTAT_API_STATISTICS + self.id_str() + "?fields=" + fields
-        if len(self._maps):
+        if self._maps:
             values = _get_json(url)["included"]["CompoundStatistics"][self.id_str()]["Values"]
         else:
             values = _get_json(url)["included"]["Statistics"][self.id_str()]["Values"]
@@ -2851,7 +2851,7 @@ def __call__(self, elt):
         """
         return self.statistic()(self.compound_map()(elt))
 
-    def id_str(self):
+    def id_str(self) -> str:
         """
         Return the padded identifier of the compound statistic.
 
@@ -2862,7 +2862,7 @@ def id_str(self):
         """
         return self._id
 
-    def _repr_(self):
+    def _repr_(self) -> str:
         """
         Return a string representation of the compound statistic.
 

src/sage/geometry/lattice_polytope.py

@@ -5060,7 +5060,7 @@ def _palp(command, polytopes, reduce_dimension=False):
     for p in polytopes:
         if p.dim() == 0:
             raise ValueError(("Cannot run \"%s\" for the zero-dimensional "
-                + "polytope!\nPolytope: %s") % (command, p))
+                              + "polytope!\nPolytope: %s") % (command, p))
         if p.dim() < p.lattice_dim():
             if not reduce_dimension:
                 raise ValueError(("Cannot run PALP for a %d-dimensional polytope " +
@@ -5075,9 +5075,9 @@ def _palp(command, polytopes, reduce_dimension=False):
               stdin=PIPE, stdout=PIPE, stderr=PIPE, close_fds=True)
     stderr = p.stderr
     err = stderr.read()
-    if len(err):
+    if err:
         raise RuntimeError(("Error executing \"%s\" for a polytope sequence!"
-            + "\nOutput:\n%s") % (command, err))
+                            + "\nOutput:\n%s") % (command, err))
     os.remove(input_file_name)
     try:
         p.terminate()
@@ -5086,7 +5086,7 @@ def _palp(command, polytopes, reduce_dimension=False):
     return output_file_name
 
 
-def _palp_canonical_order(V, PM_max, permutations):
+def _palp_canonical_order(V, PM_max, permutations) -> tuple:
     r"""
     Compute the PALP normal form of the vertices V
     using auxiliary data computed elsewhere.

src/sage/schemes/elliptic_curves/cm.py

@@ -529,7 +529,7 @@ def cm_orders(h, proof=None):
 # WAS extracted this by cutting/pasting from the pdf, and running this program:
 # z = {}
 # for X in open('/Users/wstein/tmp/a.txt').readlines():
-#    if len(X.strip()):
+#    if X.strip():
 #        v = [int(a) for a in X.split()]
 #        for i in range(5):
 #            z[v[3*i]]=(v[3*i+2], v[3*i+1])
@@ -575,7 +575,7 @@ def cm_orders(h, proof=None):
 
 # klaise_table = {}
 # for X in open('klaise_table.txt').readlines():
-#     if len(X.strip()):
+#     if X.strip():
 #         v = [int(a) for a in X.split()]
 #         for i in range(4):
 #             klaise_table[v[3*i]]=(v[3*i+2], v[3*i+1])
@@ -888,7 +888,8 @@ def discriminants_with_bounded_class_number(hmax, B=None, proof=None):
 
 @cached_function
 def is_cm_j_invariant(j, algorithm='CremonaSutherland', method=None):
-    r"""Return whether or not this is a CM `j`-invariant, and the CM discriminant if it is.
+    r"""
+    Return whether or not this is a CM `j`-invariant, and the CM discriminant if it is.
 
     INPUT:
 
@@ -910,7 +911,7 @@ def is_cm_j_invariant(j, algorithm='CremonaSutherland', method=None):
     ALGORITHM:
 
     The default algorithm used is to test whether the minimal
-    polynomial of ``j`` is a Hilbert CLass Polynomail, using
+    polynomial of ``j`` is a Hilbert CLass Polynomial, using
     :func:`is_HCP` which implements Algorithm 2 of [CreSuth2023]_ by
     Cremona and Sutherland.
 

src/sage/symbolic/ginac/inifcns_comb.cpp

@@ -105,7 +105,7 @@ static ex binomial_evalf(const ex & x, const ex & y, PyObject* parent)
 	return binomial(x, y).hold();
 }
 
-// At the moment the numeric evaluation of a binomail function always
+// At the moment the numeric evaluation of a binomial function always
 // gives a real number, but if this would be implemented using the gamma
 // function, also complex conjugation should be changed (or rather, deleted).
 static ex binomial_conjugate(const ex & x, const ex & y)

src/sage/symbolic/relation.py

@@ -1418,7 +1418,7 @@ def has_integer_assumption(v) -> bool:
         return any(isinstance(a, GenericDeclaration) and a.has(v) and
                    a._assumption in ['even', 'odd', 'integer', 'integervalued']
                    for a in alist)
-    if len(f.variables()) and all(has_integer_assumption(var) for var in f.variables()):
+    if f.variables() and all(has_integer_assumption(var) for var in f.variables()):
         return f.solve_diophantine(x, solution_dict=solution_dict)
 
     if algorithm == 'sympy':

src/sage/topology/simplicial_complex.py

@@ -2198,7 +2198,7 @@ def chain_complex(self, subcomplex=None, augmented=False,
                 # nonzero via a dictionary.
                 matrix_data = {}
                 col = 0
-                if len(old) and len(current):
+                if old and current:
                     for simplex in current:
                         for i in range(n + 1):
                             face_i = simplex.face(i)