I'm afraid you missed the joke ;-) While you believe spaces are required on both sides of an em dash, there is no consensus on this point. For example, most (but not all) American authorities say /no/ spaces should be used. That's the joke. In writing a line about "only one way to do it", I used a device (em dash) for which at least two ways to do it (with spaces, without spaces) are commonly used, neither of which is obvious -- and deliberately picked a third way just to rub it in. This will never change ;-)

This text has a line which has an ortographical typo in it. Please look at this line of text from the Zen of Python: There should be one-- and preferably only one --obvious way to do it.

Beautiful is better than ugly. Explicit is better than implicit. Simple is better than complex. Complex is better than complicated. Flat is better than nested. Sparse is better than dense. Readability counts. Special cases aren't special enough to break the rules. Although practicality beats purity. Errors should never pass silently. Unless explicitly silenced. In the face of ambiguity, refuse the temptation to guess. There should be one– and preferably only one –obvious way to do it.[a] Although that way may not be obvious at first unless you're Dutch. Now is better than never. Although never is often better than right now.[b] If the implementation is hard to explain, it's a bad idea. If the implementation is easy to explain, it may be a good idea. Namespaces are one honking great idea – let's do more of those!