python-helper: update deprecated code

Currently python-helper.py imports the imp module, but this module has
been deprecated since version 3.4 and removed in version 3.12.

Refactorize the code to handle Python versioning by moving the code at
the start of the file.

Use one block for python>=3.0, declaring the report_trace_real function.
Use a second block for python>=3.5, declaring the new_module function.

Add tests for python2 support.

Fix incorrect code using comparison to `None` instead of `cond is None`.
Reported by ruff check.

Format the code with ruff format, with line-length = 100.

src/engines/python-helper.py

@@ -4,33 +4,52 @@
 # Based on http://pymotw.com/2/sys/tracing.html, "Tracing a program as it runs"
 # and http://hg.python.org/cpython/file/2.7/Lib/trace.py
 
-import imp
 import sys
 import os
 import struct
 
 fifo_file = None
-report_trace_real = None
 
-try:
-    # In Py 2.x, the builtins were in __builtin__
-    BUILTINS = sys.modules['__builtin__']
-except KeyError:
+if sys.version_info >= (3, 0):
     # In Py 3.x, they're in builtins
-    BUILTINS = sys.modules['builtins']
+    BUILTINS = sys.modules["builtins"]
+
+    def report_trace_real(file, line):
+        size = len(file) + 1 + 8 + 4 + 4
+        data = struct.pack(
+            ">QLL%dsb" % len(file),
+            0x6D6574616C6C6775,
+            size,
+            int(line),
+            bytes(file, "utf-8"),
+            0,
+        )
+
+        fifo_file.write(data)
+else:
+    # In Py 2.x, the builtins were in __builtin__
+    BUILTINS = sys.modules["__builtin__"]
+
+    def report_trace_real(file, line):
+        size = len(file) + 1 + 8 + 4 + 4
+        data = struct.pack(">QLL%dsb" % len(file), 0x6D6574616C6C6775, size, int(line), file, 0)
 
+        fifo_file.write(data)
 
-def report_trace3(file, line):
-    size = len(file) + 1 + 8 + 4 + 4
-    data = struct.pack(">QLL%dsb" % len(file), 0x6d6574616c6c6775, size, int(line), bytes(file, 'utf-8'), 0)
 
-    fifo_file.write(data)
+if sys.version_info >= (3, 5):
+    # The imp module has been deprecated since version 3.4 and removed in
+    # version 3.12.
+    import types
 
-def report_trace2(file, line):
-    size = len(file) + 1 + 8 + 4 + 4
-    data = struct.pack(">QLL%dsb" % len(file), 0x6d6574616c6c6775, size, int(line), file, 0)
+    def new_module(name):
+        return types.ModuleType(name)
+else:
+    import imp
+
+    def new_module(name):
+        return imp.new_module(name)
 
-    fifo_file.write(data)
 
 def report_trace(file, line):
     try:
@@ -40,17 +59,19 @@ def report_trace(file, line):
         # Ignore errors
         pass
 
+
 def trace_lines(frame, event, arg):
-    if event != 'line':
+    if event != "line":
         return
     co = frame.f_code
     func_name = co.co_name
     line_no = frame.f_lineno
     filename = co.co_filename
     report_trace(filename, line_no)
 
+
 def trace_calls(frame, event, arg):
-    if event != 'call':
+    if event != "call":
         return
     co = frame.f_code
     func_name = co.co_name
@@ -59,27 +80,24 @@ def trace_calls(frame, event, arg):
     report_trace(filename, line_no)
     return trace_lines
 
+
 def runctx(cmd, globals):
     sys.settrace(trace_calls)
     try:
         exec(cmd, globals)
     finally:
         sys.settrace(None)
 
-if __name__ == "__main__":
-    if sys.version_info >= (3, 0):
-        report_trace_real = report_trace3
-    else:
-        report_trace_real = report_trace2
 
+if __name__ == "__main__":
     prog_argv = sys.argv[1:]
 
     sys.argv = prog_argv
     progname = prog_argv[0]
     sys.path[0] = os.path.split(progname)[0]
 
     fifo_path = os.getenv("KCOV_PYTHON_PIPE_PATH")
-    if fifo_path == None:
+    if fifo_path is None:
         sys.stderr.write("the KCOV_PYTHON_PIPE_PATH environment variable is not set")
         sys.exit(127)
     try:
@@ -88,9 +106,9 @@ def runctx(cmd, globals):
         sys.stderr.write("Can't open fifo file")
         sys.exit(127)
 
-    main_mod = imp.new_module('__main__')
-    old_main_mod = sys.modules['__main__']
-    sys.modules['__main__'] = main_mod
+    main_mod = new_module("__main__")
+    old_main_mod = sys.modules["__main__"]
+    sys.modules["__main__"] = main_mod
     main_mod.__file__ = progname
     main_mod.__package__ = None
     main_mod.__builtins__ = BUILTINS
@@ -99,11 +117,11 @@ def runctx(cmd, globals):
         with open(progname) as fp:
             # try to emulate __main__ namespace as much as possible
 
-            code = compile(fp.read(), progname, 'exec')
+            code = compile(fp.read(), progname, "exec")
 
             runctx(code, main_mod.__dict__)
     except IOError:
         sys.stderr.write("Cannot run file %r" % (sys.argv[0]))
         sys.exit(127)
     finally:
-        sys.modules['__main__'] = old_main_mod
+        sys.modules["__main__"] = old_main_mod

tests/tools/python.py

@@ -24,6 +24,13 @@ def runTest(self):
 
         assert b"Cannot find Python parser 'python3'" not in o
 
+class python2_can_set_legal_parser(testbase.KcovTestCase):
+    def runTest(self):
+        self.setUp()
+        rv,o = self.do(testbase.kcov + " --python-parser=python2 " + testbase.outbase + "/kcov " + testbase.sources + "/tests/python/main 5")
+
+        assert b"Cannot find Python parser 'python2'" not in o
+
 class python_issue_368_can_handle_symlink_target(testbase.KcovTestCase):
     def runTest(self):
         self.setUp()
@@ -84,6 +91,10 @@ class python3_coverage(PythonBase):
     def runTest(self):
         self.doTest("--python-parser=python3")
 
+class python2_coverage(PythonBase):
+    def runTest(self):
+        self.doTest("--python-parser=python2")
+
 class python_tricky_single_line_string_assignment(testbase.KcovTestCase):
     def runTest(self):
         self.setUp()