Get trace/debug tweaks and fixes...

Get[xx, Trace->True] was not showing all lines read. And we did not
properly hook into a changeable print function.

Using:
   import a.b.c as e

reduces unchangeable lookup (a.b.c) does not change and simplifies and
use -- e.GET_PRINT_FN as opposed to a.b.c.GET_PRINT_FN

mathics/builtin/files_io/files.py

@@ -9,7 +9,9 @@
 import tempfile
 from io import BytesIO
 
-import mathics.eval.files_io.files
+# We use the below import for access to variables that may change
+# at runtime.
+import mathics.eval.files_io.files as io_files
 from mathics.core.atoms import Integer, String, SymbolString
 from mathics.core.attributes import A_PROTECTED, A_READ_PROTECTED
 from mathics.core.builtin import (
@@ -63,7 +65,7 @@ class Input_(Predefined):
     summary_text = "the name of the current input stream"
 
     def evaluate(self, evaluation: Evaluation) -> String:
-        return String(mathics.eval.files_io.files.INPUT_VAR)
+        return String(io_files.INPUT_VAR)
 
 
 class _OpenAction(Builtin):
@@ -365,14 +367,14 @@ def eval(self, path: String, evaluation: Evaluation, options: dict):
         # Make sure to pick up copy from module each time instead of using
         # use "from ... import DEFAULT_TRACE_FN" which will not pick
         # up run-time changes made to the module function.
-        trace_fn = mathics.eval.files_io.files.DEFAULT_TRACE_FN
+        trace_fn = io_files.DEFAULT_TRACE_FN
 
         trace_get = evaluation.parse("Settings`$TraceGet")
         if (
             options["System`Trace"].to_python()
             or trace_get.evaluate(evaluation) is SymbolTrue
         ):
-            trace_fn = print_line_number_and_text
+            trace_fn = io_files.GET_PRINT_FN
 
         # perform the actual evaluation
         return eval_Get(path.value, evaluation, trace_fn)

mathics/eval/files_io/files.py

@@ -49,7 +49,13 @@ def print_line_number_and_text(line_number: int, text: str):
     """Prints a line number an text on that line with it.
     This is used as the default trace function in Get[]
     """
-    print(f"%5d: {text}" % line_number, end="")
+    if line_number == 0:
+        print(f"Reading file: {text}")
+    else:
+        print("%5d: %s" % (line_number, text.rstrip()))
+
+
+GET_PRINT_FN: Callable = print_line_number_and_text
 
 
 def set_input_var(input_string: str):