src/sage/misc/namespace_package.py (is_package_or_sage_namespace_pack…

…age_dir): New

src/sage/misc/namespace_package.py

@@ -2,6 +2,7 @@
 Utility functions for namespace packages in Sage
 """
 from importlib import import_module
+import os, glob
 
 def install_doc(package, doc):
     """
@@ -18,3 +19,47 @@ def install_doc(package, doc):
     pkg = import_module(package)
     pkg.__doc__ = doc         # enable sage.package?
     pkg.getdoc = lambda: doc  # enable help(sage.package)
+
+
+def is_package_or_sage_namespace_package_dir(path):
+    """
+    Return whether ``path`` is a directory that contains a Python package.
+
+    Ordinary Python packages are recognized by the presence of `__init__.py`.
+
+    Implicit namespace packages (PEP 420) are only recognized if they
+    follow the conventions of the Sage library, i.e., the directory contains
+    a file ``all.py`` or a file matching the pattern ``all__*.py``
+    such as ``all__sagemath_categories.py``.
+
+    EXAMPLES:
+
+    :mod:`sage.cpython` is an ordinary package::
+
+        sage: from sage.misc.namespace_package import is_package_or_sage_namespace_package_dir
+        sage: d = os.path.dirname(sage.cpython.__file__); d
+        '.../sage/cpython'
+        sage: is_package_or_sage_namespace_package_dir(d)
+        True
+
+    :mod:`sage` is designated to become an implicit namespace package::
+
+        sage: d = os.path.dirname(sage.env.__file__); d
+        '.../sage'
+        sage: is_package_or_sage_namespace_package_dir(d)
+        True
+
+    Not a package::
+
+        sage: d = os.path.join(os.path.dirname(sage.symbolic.__file__), 'ginac'); d
+        '.../sage/symbolic/ginac'
+        sage: is_package_or_sage_namespace_package_dir(d)
+        False
+    """
+    if os.path.exists(os.path.join(path, '__init__.py')):  # ordinary package
+        return True
+    if os.path.exists(os.path.join(path, 'all.py')):       # complete namespace package
+        return True
+    for _ in glob.iglob(os.path.join(path, 'all__*.py')):
+        return True                                        # partial namespace package
+    return False