extmod/modure: Add ure.sub() function and method, and tests.

This feature is controlled at compile time by MICROPY_PY_URE_SUB, disabled
by default.

Thanks to @dmazzella for the original patch for this feature; see #3770.

1 files changed, 19 insertions, 0 deletions

diff --git a/tests/extmod/ure_sub_unmatched.py b/tests/extmod/ure_sub_unmatched.py
new file mode 100644
index 000000000..4795b3196
--- /dev/null
+++ b/tests/extmod/ure_sub_unmatched.py
@@ -0,0 +1,19 @@
+# test re.sub with unmatched groups, behaviour changed in CPython 3.5
+
+try:
+    import ure as re
+except ImportError:
+    try:
+        import re
+    except ImportError:
+        print('SKIP')
+        raise SystemExit
+
+try:
+    re.sub
+except AttributeError:
+    print('SKIP')
+    raise SystemExit
+
+# first group matches, second optional group doesn't so is replaced with a blank
+print(re.sub(r'(a)(b)?', r'\2-\1', '1a2'))