implement pretty printing helper for the stdlib pprint module

...using a not-so-nice hack that only works for python 3.5+.

src/sanest/sanest.py

@@ -3,6 +3,7 @@
 import collections
 import collections.abc
 import copy
+import pprint
 import reprlib
 import sys
 
@@ -435,6 +436,31 @@ def copy(self, *, deep=False):
         return fn(self)
 
 
+def pprint_sanest_collection(
+        self, object, stream, indent, allowance, context, level):
+    """
+    Pretty-printing helper for use by the built-in pprint module.
+    """
+    opening = '{}.{.__name__}('.format(__package__, type(object))
+    stream.write(opening)
+    if type(object._data) is builtins.dict:
+        f = self._pprint_dict
+    else:
+        f = self._pprint_list
+    f(object._data, stream, indent + len(opening), allowance, context, level)
+    stream.write(')')
+
+
+# This is a hack that changes the internals of the pprint module,
+# which has no public API to register custom formatter routines.
+try:
+    dispatch_table = pprint.PrettyPrinter._dispatch
+except Exception:  # pragma: no cover
+    pass  # Python 3.4 and older do not have a dispatch table.
+else:
+    dispatch_table[SaneCollection.__repr__] = pprint_sanest_collection
+
+
 class dict(SaneCollection, collections.abc.MutableMapping):
     """
     dict-like container with support for nested lookups and type checking.

test_sanest.py

@@ -5,7 +5,9 @@
 import builtins
 import copy
 import pickle
+import pprint
 import sys
+import textwrap
 
 import pytest
 
@@ -1626,3 +1628,24 @@ def test_wrong_path_for_container_type():
 def test_missing_arg_repr():
     assert repr(_sanest.MISSING) == '<missing>'
     assert str(_sanest.MISSING) == '<missing>'
+
+
+@pytest.mark.skipif(
+    sys.version_info < (3, 5),
+    reason="requires python 3.5+ pprint module")
+def test_pretty_printing_pprint():
+    d = sanest.dict(a='a' * 30, b='b' * 30)
+    expected = textwrap.dedent("""\
+        sanest.dict({'a': 'aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa',
+                     'b': 'bbbbbbbbbbbbbbbbbbbbbbbbbbbbbb'})
+    """).rstrip()
+    actual = pprint.pformat(d)
+    assert actual == expected
+
+    l = sanest.list(['a' * 30, 'b' * 30])
+    expected = textwrap.dedent("""\
+        sanest.list(['aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa',
+                     'bbbbbbbbbbbbbbbbbbbbbbbbbbbbbb'])
+    """).rstrip()
+    actual = pprint.pformat(l)
+    assert actual == expected