Yes: >>> x = "A"*10**6 >>> x.cutprefix("B") is x True >>> x.cutprefix("") is x True >>> y = b"A"*10**6 >>> y.cutprefix(b"B") is y True >>> y.cutprefix(b"") is y True >>> z = bytearray(b"A")*10**6 >>> z.cutprefix(b"B") is z False >>> z.cutprefix(b"") is z False I'm not sure whether this should be part of the spec or an implementation detail. The (str/bytes).replace method docs don't clarify this, but they have the same behavior: >>> x = "A"*10**6 >>> x.replace("B", "C") is x True >>> x.replace("", "") is x True >>> y = b"A"*10**6 >>> y.replace(b"B", b"C") is y True >>> y.replace(b"", b"") is y True >>> z = bytearray(b"A")*10**6 >>> z.replace(b"B", b"C") is z False >>> z.replace(b"", b"") is z False