This was achieved by:
* moving many pass statements in tests onto their own lines, so they pass line coverage and can match an easy ignore pattern if branch coverage is added later.
* removing code that cannot be reached.
* removing long-disabled tests.
* removing unused code.
* adding tests for uncovered code

It turned out that removing `if __name__ == '__main__'` blocks that run unittest.main() at the bottom of test files was surprisingly contentious, so they remain and can be filtered out with an appropriate .coveragerc.

Use http.client.InvalidURL instead of ValueError as the new error case's exception.

* Implement C14N 2.0 as a new canonicalize() function in ElementTree.

Missing features:
- prefix renaming in XPath expressions (tag and attribute text is supported)
- preservation of original prefixes given redundant namespace declarations

Namespace packages _bootstrap.ModuleSpec.loader attributes are no longer `None` _after_ calling the importlib._bootstrap._init_module_attrs function.

See:
* https://stackoverflow.com/questions/52869541/namespace-package-spec-loader-and-loader-attributes-not-set-to-none
* https://bugs.python.org/issue35181

* bpo-36676: Implement namespace prefix aware parsing support for the XMLParser target in ElementTree.

* bpo-36673: Implement comment/PI parsing support for the TreeBuilder in ElementTree.

* bpo-36673: Rewrite the comment/PI factory handling for the TreeBuilder in "_elementtree" to make it use the same factories as the ElementTree module, and to make it explicit when the comments/PIs are inserted into the tree and when they are not (which is the default).

This is consistent with the rest of the `warnings.warn` usage in the
inspect.py module and aids identifying code that needs to be fixed.

This warning came in via d5d2b454

Add 3 new config methods:

* _PyCoreConfig_SetString()
* _PyCoreConfig_SetWideString()
* _PyCoreConfig_SetWideStringFromString()

Changes:

* _PyCoreConfig_Copy() returns _PyInitError.
* Add CONFIG_GET_ENV_DUP().

These tests require an SSL enabled build. Skip these tests when python is built without SSL to fix test failures.


https://bugs.python.org/issue30458

* Remove _PyInitError.user_err field and _Py_INIT_USER_ERR() macro:
  use _Py_INIT_ERR() instead. _Py_ExitInitError() now longer calls
  abort() on error: exit with exit code 1 instead.
* Add _PyInitError._type private field.
* exitcode field type is now unsigned int on Windows.
* Rename prefix field to _func.
* Rename msg field to err_msg.

Disallow control chars in http URLs in urllib.urlopen.  This addresses a potential security problem for applications that do not sanity check their URLs where http request headers could be injected.

* Add 2 new config methods:

  * _PyCoreConfig_SetArgv()
  * _PyCoreConfig_SetWideArgv()

* Add also an internal _PyCoreConfig_SetPyArgv() method.
* Remove 'args' parameter from _PyCoreConfig_Read().

Fix memory leak in Py_SetStandardStreamEncoding(): release memory
if the function is called twice.

When an attribute is deleted from a Mock, a sentinel is added rather
than just deleting the attribute. This commit checks for such sentinels
when returning the child mocks in the __dir__ method as users won't
expect deleted attributes to appear when performing dir(mock).

Initialize "stack_t current_stack" to zero using memset().

make a compare in bit-operation manner.

* bpo-36751: Deprecate getfullargspec and report positional-only args as regular args

* Use inspect.signature in testhelpers

Under some conditions the earlier fix for bpo-18075, "Infinite recursion
tests triggering a segfault on Mac OS X", now causes failures on macOS
when attempting to change stack limit with resource.setrlimit
resource.RLIMIT_STACK, like regrtest does when running the test suite.
The reverted change had specified a non-default stack size when linking
the python executable on macOS.  As of macOS 10.14.4, the previous
code causes a hard failure when running tests, although similar
failures had been seen under some conditions under some earlier
systems.  For now, revert the original change and resume using
the default stack size when linking the interpreter.

This commit implements the first version of date.fromisocalendar, the
inverse function for date.isocalendar.

This commit contains the implementation of PEP570: Python positional-only parameters.

* Update Grammar/Grammar with new typedarglist and varargslist

* Regenerate grammar files

* Update and regenerate AST related files

* Update code object

* Update marshal.c

* Update compiler and symtable

* Regenerate importlib files

* Update callable objects

* Implement positional-only args logic in ceval.c

* Regenerate frozen data

* Update standard library to account for positional-only args

* Add test file for positional-only args

* Update other test files to account for positional-only args

* Add News entry

* Update inspect module and related tests

This reverts commit b36e5d62.

* Add _PyEval_FiniThreads2(). _PyEval_FiniThreads() now only clears
  the pending lock, whereas _PyEval_FiniThreads2() destroys the GIL.
* pymain_free() now calls _PyEval_FiniThreads2().
* Py_FinalizeEx() now calls _PyEval_FiniThreads().

PyEval_AcquireLock() and PyEval_AcquireThread() now
terminate the current thread if called while the interpreter is
finalizing, making them consistent with PyEval_RestoreThread(),
Py_END_ALLOW_THREADS, and PyGILState_Ensure().