I agree that we should add a warning to these, it's easy to see how someone might read the summary of the function "Return a string of n random bytes suitable for cryptographic use." and skip over the nuance in the rest of the body of the function. Adding a red box to ensure that they know that on popular platforms os.urandom is not going to always return bytes that are suitable for cryptographic use is pretty important in my opinion. The current wording makes it sound like it's something you only need to worry about on "weird" platforms, not on one of the (if not the) most popular platforms for running Python on.