tests/cpydiff: Document format separator difference.

Signed-off-by: Jeff Epler <jepler@gmail.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/tests/cpydiff/types_str_formatsep.py b/tests/cpydiff/types_str_formatsep.py
new file mode 100644
index 000000000..05d0b8d3d
--- /dev/null
+++ b/tests/cpydiff/types_str_formatsep.py
@@ -0,0 +1,19 @@
+"""
+categories: Types,str
+description: MicroPython accepts the "," grouping option with any radix, unlike CPython
+cause: To reduce code size, MicroPython does not issue an error for this combination
+workaround: Do not use a format string like ``{:,b}`` if CPython compatibility is required.
+"""
+
+try:
+    print("{:,b}".format(99))
+except ValueError:
+    print("ValueError")
+try:
+    print("{:,x}".format(99))
+except ValueError:
+    print("ValueError")
+try:
+    print("{:,o}".format(99))
+except ValueError:
+    print("ValueError")