bpo-12915: Add pkgutil.resolve_name (GH-18310)

Lib/pkgutil.py

@@ -7,6 +7,7 @@ import importlib.util
 import importlib.machinery
 import os
 import os.path
+import re
 import sys
 from types import ModuleType
 import warnings
@@ -635,3 +636,71 @@ def get_data(package, resource):
     parts.insert(0, os.path.dirname(mod.__file__))
     resource_name = os.path.join(*parts)
     return loader.get_data(resource_name)
+
+
+_DOTTED_WORDS = r'[a-z_]\w*(\.[a-z_]\w*)*'
+_NAME_PATTERN = re.compile(f'^({_DOTTED_WORDS})(:({_DOTTED_WORDS})?)?$', re.I)
+del _DOTTED_WORDS
+
+def resolve_name(name):
+    """
+    Resolve a name to an object.
+
+    It is expected that `name` will be a string in one of the following
+    formats, where W is shorthand for a valid Python identifier and dot stands
+    for a literal period in these pseudo-regexes:
+
+    W(.W)*
+    W(.W)*:(W(.W)*)?
+
+    The first form is intended for backward compatibility only. It assumes that
+    some part of the dotted name is a package, and the rest is an object
+    somewhere within that package, possibly nested inside other objects.
+    Because the place where the package stops and the object hierarchy starts
+    can't be inferred by inspection, repeated attempts to import must be done
+    with this form.
+
+    In the second form, the caller makes the division point clear through the
+    provision of a single colon: the dotted name to the left of the colon is a
+    package to be imported, and the dotted name to the right is the object
+    hierarchy within that package. Only one import is needed in this form. If
+    it ends with the colon, then a module object is returned.
+
+    The function will return an object (which might be a module), or raise one
+    of the following exceptions:
+
+    ValueError - if `name` isn't in a recognised format
+    ImportError - if an import failed when it shouldn't have
+    AttributeError - if a failure occurred when traversing the object hierarchy
+                     within the imported package to get to the desired object)
+    """
+    m = _NAME_PATTERN.match(name)
+    if not m:
+        raise ValueError(f'invalid format: {name!r}')
+    groups = m.groups()
+    if groups[2]:
+        # there is a colon - a one-step import is all that's needed
+        mod = importlib.import_module(groups[0])
+        parts = groups[3].split('.') if groups[3] else []
+    else:
+        # no colon - have to iterate to find the package boundary
+        parts = name.split('.')
+        modname = parts.pop(0)
+        # first part *must* be a module/package.
+        mod = importlib.import_module(modname)
+        while parts:
+            p = parts[0]
+            s = f'{modname}.{p}'
+            try:
+                mod = importlib.import_module(s)
+                parts.pop(0)
+                modname = s
+            except ImportError:
+                break
+    # if we reach this point, mod is the module, already imported, and
+    # parts is the list of parts in the object hierarchy to be traversed, or
+    # an empty list if just the module is wanted.
+    result = mod
+    for p in parts:
+        result = getattr(result, p)
+    return result