ENH: Add doctest_skip_parser allowing conditional skipping of doctests

skimage/_shared/testing.py

@@ -1,6 +1,12 @@
 """Testing utilities."""
 
 
+import re
+
+
+SKIP_RE = re.compile("(\s*>>>.*?)(\s*)#\s*skip\s+if\s+(.*)$")
+
+
 def _assert_less(a, b, msg=None):
     message = "%r is not lower than %r" % (a, b)
     if msg is not None:
@@ -24,3 +30,48 @@ try:
     from nose.tools import assert_greater
 except ImportError:
     assert_greater = _assert_greater
+
+
+def doctest_skip_parser(func):
+    """ Decorator replaces custom skip test markup in doctests
+
+    Say a function has a docstring::
+
+        >>> something # skip if not HAVE_AMODULE
+        >>> something + else
+        >>> something # skip if HAVE_BMODULE
+
+    This decorator will evaluate the expresssion after ``skip if``.  If this
+    evaluates to True, then the comment is replaced by ``# doctest: +SKIP``.  If
+    False, then the comment is just removed. The expression is evaluated in the
+    ``globals`` scope of `func`.
+
+    For example, if the module global ``HAVE_AMODULE`` is False, and module
+    global ``HAVE_BMODULE`` is False, the returned function will have docstring::
+
+        >>> something # doctest: +SKIP
+        >>> something + else
+        >>> something
+
+    """
+    lines = func.__doc__.split('\n')
+    new_lines = []
+    for line in lines:
+        match = SKIP_RE.match(line)
+        if match is None:
+            new_lines.append(line)
+            continue
+        code, space, expr = match.groups()
+
+        try:
+            # Works as a function decorator
+            if eval(expr, func.__globals__):
+                code = code + space + "# doctest: +SKIP"
+        except AttributeError:
+            # Works as a class decorator
+            if eval(expr, func.__init__.__globals__):
+                code = code + space + "# doctest: +SKIP"
+
+        new_lines.append(code)
+    func.__doc__ = "\n".join(new_lines)
+    return func