Hi, On Mon, May 24, 2021 at 12:26 AM hw <h...@adminart.net> wrote: > > On 5/23/21 10:02 PM, Stestagg wrote: > > > > > > On Sun, 23 May 2021 at 20:37, hw <h...@adminart.net > > <mailto:h...@adminart.net>> wrote: > > > > On 5/23/21 7:28 PM, Peter Otten wrote: > > > On 23/05/2021 06:37, hw wrote: > > >> > > >> Hi, > > >> > > >> I'm starting to learn python and have made a little example program > > >> following a tutorial[1] I'm attaching. > > >> > > >> Running it, I'm getting: > > >> > > >> > > >> Traceback (most recent call last): > > >> File "[...]/hworld.py", line 18, in <module> > > >> print(isinstance(int, float)) > > >> TypeError: isinstance() arg 2 must be a type or tuple of types > > >> > > >> > > >> I would understand to get an error message in line 5 but not in 18. > > >> Is this a bug or a feature? > > > > > > It is a bug in your code (which you don't provide). Did you > > assign some > > > value to float, e. g.: > > > > > > >>> float = 42.0 > > > >>> isinstance(int, float) > > > Traceback (most recent call last): > > > File "<pyshell#313>", line 1, in <module> > > > isinstance(int, float) > > > TypeError: isinstance() arg 2 must be a type or tuple of types > > > > > > If you do not shadow the built-in you should get > > > > > > >>> isinstance(int, float) > > > False > > > > > > > Apparently the attachment was stripped from my message. I'll put a > > smaller version directly into this message instead of an attachment: > > > > > > #!/usr/bin/python > > > > print("world!") > > > > int = 17 > > print("world", int) > > > > float = 6.670 > > print("world", float) > > > > foo = 0 > > print(type(int)) > > print(type(float)) > > print(type(foo)) > > > > print(isinstance(foo, str)) > > print(isinstance(int, float)) > > print(isinstance(float, float)) > > > > > > I don't know about shadowing. > > > > > > Shadowing is effectively saying “within this bit of code, (scope) I’m > > going to use an already-used name for my own value” > > That should give at least a warning. > > > If I have defeated a whole variable type > > by naming a variable like a variable type, I would think it is a bad > > idea for python to allow this without warning. > > > > > > There are some reasons why allowing this is quite nice. And there’s > > actually a ton of corner cases to consider when thinking about changing > > the rules > > Perl has a way to turn off unwanted warnings. It won't change the rules > to give a warning. > > > Interestingly python 3 made this a little bit better by stopping you > > from rebinding (shadowing) a number of built ins, such as True and False. > > > > In your case, I agree that it is super confusing. > > It seems dangerous and seems to show that python is too unfinished to be > used. For all I know, it makes it easy to, for example, drop a whole > table in a database because something was shadowed without warning. > > I can imagine that there can be all kinds of situations in which > something like that happens, and you can spend hours or days trying to > figure out what's wrong and may never find it. > > > One thing to learn to > > look out for is if you assign to a name, then use that name on a > > different context, expecting it to be different, then that’s not likely > > to work as you expect. > > Then why doesn't give it at least a warning? > > There is even no indication from the output from the program before it > aborts with an error message that something might be wrong: For > 'type(float)', it prints "<class 'float'>" just like it does for int. > How is anyone supposed to debug stuff like that? > > Why doesn't print(type(float)) give an error message after the variable > type was already defeated (or prints something else)? What is it > actually printing? > > > It seems like a recipie > > for creating chaos. > > > > > > Luckily almost every python code checker and/or linter will highlight > > this for you. > > > > If you’re learning python, I’d highly recommend doing so in an ide or > > editor that has a code checker running. > > Emcas highlights the syntax fine; I don't know if it can do more for > python. It shouldn't need to. > > Things get creepy when a programming language makes it so that the > programmer can't figure out anymore how a result produced by his program > has come about.
Remember - python is an untyped language. It is not C, C++ or even Pascal. So there is no difference whether you write float = 5.0 or float1 = 5.0 Thank you. > -- > https://mail.python.org/mailman/listinfo/python-list -- https://mail.python.org/mailman/listinfo/python-list
