Python: Address review comments

Renames the methods to include the word `Positional`, and adds
documentation for the behaviour of `getMaxPositionalArguments` when the
function in question has a `*varargs` parameter (and hence no upper
limit on the number of arguments).

python/ql/lib/semmle/python/Function.qll

@@ -165,12 +165,18 @@ class Function extends Function_, Scope, AstNode {
   }
 
   /** Gets the minimum number of positional arguments that can be correctly passed to this function. */
-  int getMinArguments() {
+  int getMinPositionalArguments() {
     result = count(this.getAnArg()) - count(this.getDefinition().getArgs().getADefault())
   }
 
-  /** Gets the maximum number of positional arguments that can be correctly passed to this function. */
-  int getMaxArguments() {
+  /**
+   * Gets the maximum number of positional arguments that can be correctly passed to this function.
+   *
+   * If the function has a `*vararg` parameter, there is no upper limit on the number of positional
+   * arguments that can be passed to the function. In this case, this method returns a very large
+   * number (currently `INT_MAX`, 2147483647, but this may change in the future).
+   */
+  int getMaxPositionalArguments() {
     if exists(this.getVararg())
     then result = 2147483647 // INT_MAX
     else result = count(this.getAnArg())

python/ql/lib/semmle/python/objects/ObjectAPI.qll

@@ -738,9 +738,9 @@ class PythonFunctionValue extends FunctionValue {
     else result = "function " + this.getQualifiedName()
   }
 
-  override int minParameters() { result = this.getScope().getMinArguments() }
+  override int minParameters() { result = this.getScope().getMinPositionalArguments() }
 
-  override int maxParameters() { result = this.getScope().getMaxArguments() }
+  override int maxParameters() { result = this.getScope().getMaxPositionalArguments() }
 
   /** Gets a control flow node corresponding to a return statement in this function */
   ControlFlowNode getAReturnedNode() { result = this.getScope().getAReturnValueFlowNode() }

python/ql/src/Functions/SignatureSpecialMethods.ql

@@ -40,23 +40,25 @@ predicate is_ternary_op(string name) {
 
 predicate is_quad_op(string name) { name = "__setslice__" or name = "__exit__" }
 
-int argument_count(PythonFunctionValue f, string name, ClassValue cls) {
-  cls.declaredAttribute(name) = f and
-  (
-    is_unary_op(name) and result = 1
-    or
-    is_binary_op(name) and result = 2
-    or
-    is_ternary_op(name) and result = 3
-    or
-    is_quad_op(name) and result = 4
-  )
+int argument_count(string name) {
+  is_unary_op(name) and result = 1
+  or
+  is_binary_op(name) and result = 2
+  or
+  is_ternary_op(name) and result = 3
+  or
+  is_quad_op(name) and result = 4
+}
+
+predicate declaredAttributeVar(Class cls, string name, EssaVariable var) {
+  name = var.getName() and
+  pragma[only_bind_into](pragma[only_bind_into](var).getAUse()) = cls.getANormalExit()
 }
 
 predicate incorrect_special_method_defn(
   PythonFunctionValue func, string message, boolean show_counts, string name, ClassValue owner
 ) {
-  exists(int required | required = argument_count(func, name, owner) |
+  exists(int required | required = argument_count(name) and owner.declaredAttribute(name) = func |
     /* actual_non_default <= actual */
     if required > func.maxParameters()
     then message = "Too few parameters" and show_counts = true
@@ -104,7 +106,9 @@ predicate incorrect_get(FunctionValue func, string message, boolean show_counts,
 }
 
 string should_have_parameters(PythonFunctionValue f, string name, ClassValue owner) {
-  exists(int i | i = argument_count(f, name, owner) | result = i.toString())
+  exists(int i | i = argument_count(name) and owner.declaredAttribute(name) = f |
+    result = i.toString()
+  )
   or
   owner.declaredAttribute(name) = f and
   (name = "__get__" or name = "__pow__") and