refactor: remove unneeded backward.py shims

Removed were:

- StringIO
- configparser
- string_class
- unicode_class
- range
- zip_longest
- get_thread_id
- path_types
- shlex_quote
- reprlib

16 files changed, 53 insertions, 123 deletions

diff --git a/coverage/backward.py b/coverage/backward.py
index da839d71..15f4e88a 100644
--- a/coverage/backward.py
+++ b/coverage/backward.py
@@ -3,84 +3,8 @@
 
 """Add things to old Pythons so I can pretend they are newer."""
 
-# This file's purpose is to provide modules to be imported from here.
-# pylint: disable=unused-import
-
-import os
 import sys
 
-from datetime import datetime
-
-
-# Pythons 2 and 3 differ on where to get StringIO.
-try:
-    from cStringIO import StringIO
-except ImportError:
-    from io import StringIO
-
-# In py3, ConfigParser was renamed to the more-standard configparser.
-# But there's a py3 backport that installs "configparser" in py2, and I don't
-# want it because it has annoying deprecation warnings. So try the real py2
-# import first.
-try:
-    import ConfigParser as configparser
-except ImportError:
-    import configparser
-
-# What's a string called?
-try:
-    string_class = basestring
-except NameError:
-    string_class = str
-
-# What's a Unicode string called?
-try:
-    unicode_class = unicode
-except NameError:
-    unicode_class = str
-
-# range or xrange?
-try:
-    range = xrange      # pylint: disable=redefined-builtin
-except NameError:
-    range = range
-
-try:
-    from itertools import zip_longest
-except ImportError:
-    from itertools import izip_longest as zip_longest
-
-# Where do we get the thread id from?
-try:
-    from thread import get_ident as get_thread_id
-except ImportError:
-    from threading import get_ident as get_thread_id
-
-try:
-    os.PathLike
-except AttributeError:
-    # This is Python 2 and 3
-    path_types = (bytes, string_class, unicode_class)
-else:
-    # 3.6+
-    path_types = (bytes, str, os.PathLike)
-
-# shlex.quote is new, but there's an undocumented implementation in "pipes",
-# who knew!?
-try:
-    from shlex import quote as shlex_quote
-except ImportError:
-    # Useful function, available under a different (undocumented) name
-    # in Python versions earlier than 3.3.
-    from pipes import quote as shlex_quote
-
-try:
-    import reprlib
-except ImportError:             # pragma: not covered
-    # We need this on Python 2, but in testing environments, a backport is
-    # installed, so this import isn't used.
-    import repr as reprlib
-
 # A function to iterate listlessly over a dict's items, and one to get the
 # items as a list.
 try:
diff --git a/coverage/collector.py b/coverage/collector.py
index a4f1790d..17dcac1c 100644
--- a/coverage/collector.py
+++ b/coverage/collector.py
@@ -7,7 +7,7 @@ import os
 import sys
 
 from coverage import env
-from coverage.backward import litems, range     # pylint: disable=redefined-builtin
+from coverage.backward import litems
 from coverage.debug import short_stack
 from coverage.disposition import FileDisposition
 from coverage.misc import CoverageException, isolate_module
diff --git a/coverage/config.py b/coverage/config.py
index a48251fb..7bfc74db 100644
--- a/coverage/config.py
+++ b/coverage/config.py
@@ -4,13 +4,14 @@
 """Config file for coverage.py"""
 
 import collections
+import configparser
 import copy
 import os
 import os.path
 import re
 
 from coverage import env
-from coverage.backward import configparser, iitems, string_class
+from coverage.backward import iitems
 from coverage.misc import contract, CoverageException, isolate_module
 from coverage.misc import substitute_variables
 
@@ -247,7 +248,7 @@ class CoverageConfig(object):
         """Read config values from `kwargs`."""
         for k, v in iitems(kwargs):
             if v is not None:
-                if k in self.MUST_BE_LIST and isinstance(v, string_class):
+                if k in self.MUST_BE_LIST and isinstance(v, str):
                     v = [v]
                 setattr(self, k, v)
 
diff --git a/coverage/control.py b/coverage/control.py
index 1623b093..5c5d13aa 100644
--- a/coverage/control.py
+++ b/coverage/control.py
@@ -14,7 +14,7 @@ import time
 
 from coverage import env
 from coverage.annotate import AnnotateReporter
-from coverage.backward import string_class, iitems
+from coverage.backward import iitems
 from coverage.collector import Collector, CTracer
 from coverage.config import read_coverage_config
 from coverage.context import should_start_context_test_function, combine_context_switchers
@@ -465,7 +465,7 @@ class Coverage(object):
 
         suffix = self._data_suffix_specified
         if suffix or self.config.parallel:
-            if not isinstance(suffix, string_class):
+            if not isinstance(suffix, str):
                 # if data_suffix=True, use .machinename.pid.random
                 suffix = True
         else:
@@ -812,7 +812,7 @@ class Coverage(object):
         plugin = None
         file_reporter = "python"
 
-        if isinstance(morf, string_class):
+        if isinstance(morf, str):
             mapped_morf = self._file_mapper(morf)
             plugin_name = self._data.file_tracer(mapped_morf)
             if plugin_name:
diff --git a/coverage/debug.py b/coverage/debug.py
index 194f16f5..efcaca2a 100644
--- a/coverage/debug.py
+++ b/coverage/debug.py
@@ -6,16 +6,17 @@
 import contextlib
 import functools
 import inspect
+import io
 import itertools
 import os
 import pprint
+import reprlib
 import sys
 try:
     import _thread
 except ImportError:
     import thread as _thread
 
-from coverage.backward import reprlib, StringIO
 from coverage.misc import isolate_module
 
 os = isolate_module(os)
@@ -86,7 +87,7 @@ class DebugControl(object):
 class DebugControlString(DebugControl):
     """A `DebugControl` that writes to a StringIO, for testing."""
     def __init__(self, options):
-        super(DebugControlString, self).__init__(options, StringIO())
+        super(DebugControlString, self).__init__(options, io.StringIO())
 
     def get_output(self):
         """Get the output text from the `DebugControl`."""
diff --git a/coverage/misc.py b/coverage/misc.py
index 44d1cdf8..148f42e1 100644
--- a/coverage/misc.py
+++ b/coverage/misc.py
@@ -16,7 +16,7 @@ import sys
 import types
 
 from coverage import env
-from coverage.backward import to_bytes, unicode_class
+from coverage.backward import to_bytes
 
 ISOLATED_MODULES = {}
 
@@ -71,7 +71,7 @@ if USE_CONTRACTS:
 
     # Define contract words that PyContract doesn't have.
     new_contract('bytes', lambda v: isinstance(v, bytes))
-    new_contract('unicode', lambda v: isinstance(v, unicode_class))
+    new_contract('unicode', lambda v: isinstance(v, str))
 
     def one_of(argnames):
         """Ensure that only one of the argnames is non-None."""
@@ -204,7 +204,7 @@ class Hasher(object):
     def update(self, v):
         """Add `v` to the hash, recursively if needed."""
         self.md5.update(to_bytes(str(type(v))))
-        if isinstance(v, unicode_class):
+        if isinstance(v, str):
             self.md5.update(v.encode('utf8'))
         elif isinstance(v, bytes):
             self.md5.update(v)
diff --git a/coverage/numbits.py b/coverage/numbits.py
index 7205b9f1..7a17fc56 100644
--- a/coverage/numbits.py
+++ b/coverage/numbits.py
@@ -15,7 +15,9 @@ the future.  Use these functions to work with those binary blobs of data.
 """
 import json
 
-from coverage.backward import byte_to_int, bytes_to_ints, binary_bytes, zip_longest
+from itertools import zip_longest
+
+from coverage.backward import byte_to_int, bytes_to_ints, binary_bytes
 from coverage.misc import contract, new_contract
 
 def _to_blob(b):
diff --git a/coverage/parser.py b/coverage/parser.py
index 6280129c..abcda5fb 100644
--- a/coverage/parser.py
+++ b/coverage/parser.py
@@ -11,8 +11,7 @@ import token
 import tokenize
 
 from coverage import env
-from coverage.backward import range    # pylint: disable=redefined-builtin
-from coverage.backward import bytes_to_ints, string_class
+from coverage.backward import bytes_to_ints
 from coverage.bytecode import code_objects
 from coverage.debug import short_stack
 from coverage.misc import contract, join_regex, new_contract, nice_pair, one_of
@@ -1206,7 +1205,7 @@ if AST_DUMP:            # pragma: debugging
         """Is `value` simple enough to be displayed on a single line?"""
         return (
             value in [None, [], (), {}, set()] or
-            isinstance(value, (string_class, int, float))
+            isinstance(value, (str, int, float))
         )
 
     def ast_dump(node, depth=0):
diff --git a/coverage/sqldata.py b/coverage/sqldata.py
index 62df6508..9af08030 100644
--- a/coverage/sqldata.py
+++ b/coverage/sqldata.py
@@ -14,9 +14,10 @@ import os
 import re
 import sqlite3
 import sys
+import threading
 import zlib
 
-from coverage.backward import get_thread_id, iitems, to_bytes, to_string
+from coverage.backward import iitems, to_bytes, to_string
 from coverage.debug import NoDebugging, SimpleReprMixin, clipped_repr
 from coverage.files import PathAliases
 from coverage.misc import CoverageException, contract, file_be_gone, filename_suffix, isolate_module
@@ -244,7 +245,7 @@ class CoverageData(SimpleReprMixin):
         """
         if self._debug.should('dataio'):
             self._debug.write("Creating data file {!r}".format(self._filename))
-        self._dbs[get_thread_id()] = db = SqliteDb(self._filename, self._debug)
+        self._dbs[threading.get_ident()] = db = SqliteDb(self._filename, self._debug)
         with db:
             db.executescript(SCHEMA)
             db.execute("insert into coverage_schema (version) values (?)", (SCHEMA_VERSION,))
@@ -261,12 +262,12 @@ class CoverageData(SimpleReprMixin):
         """Open an existing db file, and read its metadata."""
         if self._debug.should('dataio'):
             self._debug.write("Opening data file {!r}".format(self._filename))
-        self._dbs[get_thread_id()] = SqliteDb(self._filename, self._debug)
+        self._dbs[threading.get_ident()] = SqliteDb(self._filename, self._debug)
         self._read_db()
 
     def _read_db(self):
         """Read the metadata from a database so that we are ready to use it."""
-        with self._dbs[get_thread_id()] as db:
+        with self._dbs[threading.get_ident()] as db:
             try:
                 schema_version, = db.execute_one("select version from coverage_schema")
             except Exception as exc:
@@ -292,15 +293,15 @@ class CoverageData(SimpleReprMixin):
 
     def _connect(self):
         """Get the SqliteDb object to use."""
-        if get_thread_id() not in self._dbs:
+        if threading.get_ident() not in self._dbs:
             if os.path.exists(self._filename):
                 self._open_db()
             else:
                 self._create_db()
-        return self._dbs[get_thread_id()]
+        return self._dbs[threading.get_ident()]
 
     def __nonzero__(self):
-        if (get_thread_id() not in self._dbs and not os.path.exists(self._filename)):
+        if (threading.get_ident() not in self._dbs and not os.path.exists(self._filename)):
             return False
         try:
             with self._connect() as con:
@@ -357,7 +358,7 @@ class CoverageData(SimpleReprMixin):
                 "Unrecognized serialization: {!r} (head of {} bytes)".format(data[:40], len(data))
                 )
         script = to_string(zlib.decompress(data[1:]))
-        self._dbs[get_thread_id()] = db = SqliteDb(self._filename, self._debug)
+        self._dbs[threading.get_ident()] = db = SqliteDb(self._filename, self._debug)
         with db:
             db.executescript(script)
         self._read_db()
diff --git a/coverage/tomlconfig.py b/coverage/tomlconfig.py
index 3ad58157..5f8c154d 100644
--- a/coverage/tomlconfig.py
+++ b/coverage/tomlconfig.py
@@ -3,12 +3,12 @@
 
 """TOML configuration support for coverage.py"""
 
+import configparser
 import io
 import os
 import re
 
 from coverage import env
-from coverage.backward import configparser, path_types
 from coverage.misc import CoverageException, substitute_variables
 
 # TOML support is an install-time extra option.
@@ -37,7 +37,7 @@ class TomlConfigParser:
     def read(self, filenames):
         # RawConfigParser takes a filename or list of filenames, but we only
         # ever call this with a single filename.
-        assert isinstance(filenames, path_types)
+        assert isinstance(filenames, (bytes, str, os.PathLike))
         filename = filenames
         if env.PYVERSION >= (3, 6):
             filename = os.fspath(filename)
diff --git a/tests/coveragetest.py b/tests/coveragetest.py
index 415dd4ab..2a55cf8b 100644
--- a/tests/coveragetest.py
+++ b/tests/coveragetest.py
@@ -7,6 +7,7 @@ import contextlib
 import datetime
 import difflib
 import glob
+import io
 import os
 import os.path
 import random
@@ -18,7 +19,7 @@ import pytest
 
 import coverage
 from coverage import env
-from coverage.backward import StringIO, import_local_file, string_class, shlex_quote
+from coverage.backward import import_local_file
 from coverage.cmdline import CoverageScript
 
 from tests.helpers import arcs_to_arcz_repr, arcz_to_arcs, assert_count_equal
@@ -176,7 +177,7 @@ class CoverageTest(
                     assert False, "None of the lines choices matched %r" % (statements,)
 
             missing_formatted = analysis.missing_formatted()
-            if isinstance(missing, string_class):
+            if isinstance(missing, str):
                 msg = "{!r} != {!r}".format(missing_formatted, missing)
                 assert missing_formatted == missing, msg
             else:
@@ -202,7 +203,7 @@ class CoverageTest(
                 assert False, msg
 
         if report:
-            frep = StringIO()
+            frep = io.StringIO()
             cov.report(mod, file=frep, show_missing=True)
             rep = " ".join(frep.getvalue().split("\n")[2].split()[1:])
             assert report == rep, "{!r} != {!r}".format(report, rep)
@@ -380,7 +381,7 @@ class CoverageTest(
         else:
             command_words = [command_name]
 
-        cmd = " ".join([shlex_quote(w) for w in command_words] + command_args)
+        cmd = " ".join([shlex.quote(w) for w in command_words] + command_args)
 
         # Add our test modules directory to PYTHONPATH.  I'm sure there's too
         # much path munging here, but...
diff --git a/tests/test_api.py b/tests/test_api.py
index f24beaf4..6eff06fe 100644
--- a/tests/test_api.py
+++ b/tests/test_api.py
@@ -5,6 +5,7 @@
 
 import fnmatch
 import glob
+import io
 import os
 import os.path
 import re
@@ -16,7 +17,7 @@ import pytest
 
 import coverage
 from coverage import env
-from coverage.backward import code_object, import_local_file, StringIO
+from coverage.backward import code_object, import_local_file
 from coverage.data import line_counts
 from coverage.files import abs_file, relative_filename
 from coverage.misc import CoverageException
@@ -945,7 +946,7 @@ class ReportIncludeOmitTest(IncludeOmitTestsMixin, CoverageTest):
         cov.start()
         import usepkgs  # pragma: nested   # pylint: disable=import-error, unused-import
         cov.stop()      # pragma: nested
-        report = StringIO()
+        report = io.StringIO()
         cov.report(file=report, **kwargs)
         return report.getvalue()
 
@@ -1070,7 +1071,7 @@ class TestRunnerPluginTest(CoverageTest):
         self.start_import_stop(cov, "prog")
         cov.combine()
         cov.save()
-        report = StringIO()
+        report = io.StringIO()
         cov.report(show_missing=None, ignore_errors=True, file=report, skip_covered=None,
                    skip_empty=None)
         assert report.getvalue() == textwrap.dedent("""\
diff --git a/tests/test_debug.py b/tests/test_debug.py
index cb83e519..50f191c6 100644
--- a/tests/test_debug.py
+++ b/tests/test_debug.py
@@ -3,6 +3,7 @@
 
 """Tests of coverage/debug.py"""
 
+import io
 import os
 import re
 
@@ -10,7 +11,6 @@ import pytest
 
 import coverage
 from coverage import env
-from coverage.backward import StringIO
 from coverage.debug import filter_text, info_formatter, info_header, short_id, short_stack
 from coverage.debug import clipped_repr
 
@@ -106,7 +106,7 @@ class DebugTraceTest(CoverageTest):
                 f1(i)
             """)
 
-        debug_out = StringIO()
+        debug_out = io.StringIO()
         cov = coverage.Coverage(debug=debug)
         cov._debug_file = debug_out
         self.start_import_stop(cov, "f1")
diff --git a/tests/test_html.py b/tests/test_html.py
index c0413c5a..c561a5d2 100644
--- a/tests/test_html.py
+++ b/tests/test_html.py
@@ -16,7 +16,6 @@ import mock
 import pytest
 
 import coverage
-from coverage.backward import unicode_class
 from coverage import env
 from coverage.files import abs_file, flat_rootname
 import coverage.html
@@ -629,12 +628,12 @@ def compare_html(expected, actual):
         (r'<span class="(nam|key)">(print|True|False)</span>', r'<span class="nam">\2</span>'),
         # Occasionally an absolute path is in the HTML report.
         (filepath_to_regex(TESTS_DIR), 'TESTS_DIR'),
-        (filepath_to_regex(flat_rootname(unicode_class(TESTS_DIR))), '_TESTS_DIR'),
+        (filepath_to_regex(flat_rootname(str(TESTS_DIR))), '_TESTS_DIR'),
         # The temp dir the tests make.
         (filepath_to_regex(os.getcwd()), 'TEST_TMPDIR'),
-        (filepath_to_regex(flat_rootname(unicode_class(os.getcwd()))), '_TEST_TMPDIR'),
+        (filepath_to_regex(flat_rootname(str(os.getcwd()))), '_TEST_TMPDIR'),
         (filepath_to_regex(abs_file(os.getcwd())), 'TEST_TMPDIR'),
-        (filepath_to_regex(flat_rootname(unicode_class(abs_file(os.getcwd())))), '_TEST_TMPDIR'),
+        (filepath_to_regex(flat_rootname(str(abs_file(os.getcwd())))), '_TEST_TMPDIR'),
         (r'/private/var/folders/[\w/]{35}/coverage_test/tests_test_html_\w+_\d{8}', 'TEST_TMPDIR'),
         (r'_private_var_folders_\w{35}_coverage_test_tests_test_html_\w+_\d{8}', '_TEST_TMPDIR'),
     ]
diff --git a/tests/test_plugins.py b/tests/test_plugins.py
index 59be645c..5a8d92ee 100644
--- a/tests/test_plugins.py
+++ b/tests/test_plugins.py
@@ -4,6 +4,7 @@
 """Tests for plugins."""
 
 import inspect
+import io
 import os.path
 from xml.etree import ElementTree
 
@@ -11,7 +12,7 @@ import pytest
 
 import coverage
 from coverage import env
-from coverage.backward import StringIO, import_local_file
+from coverage.backward import import_local_file
 from coverage.data import line_counts
 from coverage.control import Plugins
 from coverage.misc import CoverageException
@@ -188,7 +189,7 @@ class PluginTest(CoverageTest):
             def coverage_init(reg, options):
                 reg.add_file_tracer(Plugin())
             """)
-        debug_out = StringIO()
+        debug_out = io.StringIO()
         cov = coverage.Coverage(debug=["sys"])
         cov._debug_file = debug_out
         cov.set_option("run:plugins", ["plugin_sys_info"])
@@ -218,7 +219,7 @@ class PluginTest(CoverageTest):
             def coverage_init(reg, options):
                 reg.add_configurer(Plugin())
             """)
-        debug_out = StringIO()
+        debug_out = io.StringIO()
         cov = coverage.Coverage(debug=["sys"])
         cov._debug_file = debug_out
         cov.set_option("run:plugins", ["plugin_no_sys_info"])
@@ -411,7 +412,7 @@ class GoodFileTracerTest(FileTracerTest):
 
         self.start_import_stop(cov, "caller")
 
-        repout = StringIO()
+        repout = io.StringIO()
         total = cov.report(file=repout, include=["*.html"], omit=["uni*.html"], show_missing=True)
         report = repout.getvalue().splitlines()
         expected = [
@@ -511,7 +512,7 @@ class GoodFileTracerTest(FileTracerTest):
         cov.set_option("run:plugins", ["fairly_odd_plugin"])
         self.start_import_stop(cov, "unsuspecting")
 
-        repout = StringIO()
+        repout = io.StringIO()
         total = cov.report(file=repout, show_missing=True)
         report = repout.getvalue().splitlines()
         expected = [
diff --git a/tests/test_summary.py b/tests/test_summary.py
index b6405bff..b00ee96b 100644
--- a/tests/test_summary.py
+++ b/tests/test_summary.py
@@ -5,6 +5,7 @@
 """Test text-based summary reporting for coverage.py"""
 
 import glob
+import io
 import os
 import os.path
 import py_compile
@@ -13,7 +14,6 @@ import re
 import pytest
 
 import coverage
-from coverage.backward import StringIO
 from coverage import env
 from coverage.control import Coverage
 from coverage.data import CoverageData
@@ -655,7 +655,7 @@ class SummaryTest(UsingModulesMixin, CoverageTest):
 
     def get_report(self, cov):
         """Get the report from `cov`, and canonicalize it."""
-        repout = StringIO()
+        repout = io.StringIO()
         cov.report(file=repout, show_missing=False)
         report = repout.getvalue().replace('\\', '/')
         report = re.sub(r" +", " ", report)
@@ -779,7 +779,7 @@ class SummaryTest(UsingModulesMixin, CoverageTest):
         import usepkgs  # pragma: nested # pylint: disable=import-error, unused-import
         cov.stop()      # pragma: nested
 
-        repout = StringIO()
+        repout = io.StringIO()
         cov.report(file=repout, show_missing=False)
 
         report = repout.getvalue().replace('\\', '/')
@@ -857,7 +857,7 @@ class SummaryReporterConfigurationTest(CoverageTest):
         for name, value in options:
             cov.set_option(name, value)
         printer = SummaryReporter(cov)
-        destination = StringIO()
+        destination = io.StringIO()
         printer.report([], destination)
         return destination.getvalue()