1 files changed, 64 insertions, 0 deletions
diff --git a/lib/testtools/testtools/helpers.py b/lib/testtools/testtools/helpers.py
new file mode 100644
index 0000000000..0f489c73f6
--- /dev/null
+++ b/lib/testtools/testtools/helpers.py
@@ -0,0 +1,64 @@
+# Copyright (c) 2010 Jonathan M. Lange. See LICENSE for details.
+
+__all__ = [
+    'try_import',
+    'try_imports',
+    ]
+
+
+def try_import(name, alternative=None):
+    """Attempt to import `name`.  If it fails, return `alternative`.
+
+    When supporting multiple versions of Python or optional dependencies, it
+    is useful to be able to try to import a module.
+
+    :param name: The name of the object to import, e.g. 'os.path' or
+        'os.path.join'.
+    :param alternative: The value to return if no module can be imported.
+        Defaults to None.
+    """
+    module_segments = name.split('.')
+    while module_segments:
+        module_name = '.'.join(module_segments)
+        try:
+            module = __import__(module_name)
+        except ImportError:
+            module_segments.pop()
+            continue
+        else:
+            break
+    else:
+        return alternative
+    nonexistent = object()
+    for segment in name.split('.')[1:]:
+        module = getattr(module, segment, nonexistent)
+        if module is nonexistent:
+            return alternative
+    return module
+
+
+_RAISE_EXCEPTION = object()
+def try_imports(module_names, alternative=_RAISE_EXCEPTION):
+    """Attempt to import modules.
+
+    Tries to import the first module in `module_names`.  If it can be
+    imported, we return it.  If not, we go on to the second module and try
+    that.  The process continues until we run out of modules to try.  If none
+    of the modules can be imported, either raise an exception or return the
+    provided `alternative` value.
+
+    :param module_names: A sequence of module names to try to import.
+    :param alternative: The value to return if no module can be imported.
+        If unspecified, we raise an ImportError.
+    :raises ImportError: If none of the modules can be imported and no
+        alternative value was specified.
+    """
+    module_names = list(module_names)
+    for module_name in module_names:
+        module = try_import(module_name)
+        if module:
+            return module
+    if alternative is _RAISE_EXCEPTION:
+        raise ImportError(
+            "Could not import any of: %s" % ', '.join(module_names))
+    return alternative