Op 18-09-17 om 14:58 schreef Chris Angelico: > On Mon, Sep 18, 2017 at 10:42 PM, Rick Johnson > <rantingrickjohn...@gmail.com> wrote: >> (2) Python is, in essence, converting the source code >> syntax of: >> >> if someObject: >> >> to: >> >> if BOOLEAN_VALUE_OF_SOMEOBJECT: >> >> Which, although the result of such a conversion (a >> Boolean) will be perfectly symmetrical with formal logic >> statements, the conversion is not obvious, because it >> happens behind the curtains. > What a surprise. In the context of a statement that has exactly two > possible courses of action (either you go into the 'if' block, or you > go into the 'else' block (if any)), you use the boolean value of an > object. What part of this is not obvious?
Well that you reduce an object to a boolean value is not obvious to begin with. A TypeError because you are treating a non-boolean as a boolean would have been more obvious to me. A second thought is that it isn't obvious that empty strings, lists ... should be thought of as falsy. Sometimes I am treating a stream of values/objects and when I ask for the next available items, i get a string/list. An empty string/list in that context would mean that nothing was available, but it is possible that more will be available later and so could be treated just like a non-empty list/string. But then, I can't mix this kind of interface with the io module because a read from classes in that module will produce an empty (byte)string to indicate the end of the stream. Once you understand how python does things, you can work with it, but IMO the way python does things is IMO not at all that obvious as people would like us to think. -- Antoon Pardon. -- https://mail.python.org/mailman/listinfo/python-list
