What’s New in Python 3.8

Post by eesmith » Tue, Oct 15, 2019, 10:22 AM UTC

drdaeman wrote: post #86

geofft wrote: post #69

Earlier quoted context omitted.

> The "walrus operator" will occasionally be useful, but I doubt I will find many effective uses for it. The primary one I want is if m := re.match(...): print(m.group(1)) and while s := network_service.read(): process(s) both of which are both clearer and less error-prone than their non-walrus variants. The other one that I would have found useful an hour ago is in interactive exploration with comprehensions. I freq…

Coming from Perl, I used to want this badly, but then I thought that there's absolutely nothing wrong with m = re.match(...) if m is not None: pass Now, I wonder what you meant saying that single-line version is less error-prone, because I don't think so. I believe they're exactly the same in this regard, except for a bizarre case when someone would bastardize the code by putting some irrelevant lines between the ass…

    for line in f:
      if (m:= pat1.search(line)) is not None:
        ... do stuff ..
      elif (m:= pat2.search(line)) is not None:
        ... do other stuff ..
      elif (m:= pat3.search(line)) is not None:
         ... do something else ..

    for line in f:
      m = pat1.search(line)
      if m is not None:
        ... do stuff ..
      else:
        m = pat2.search(line)
        if m is not None:
          ... do other stuff ..
        else:
           m = pat3.search(line)
           if m is not None:
             ... do something else ..

Post by eesmith » Tue, Oct 15, 2019, 10:32 AM UTC

est wrote: post #112

geofft wrote: post #69

Earlier quoted context omitted.

> The "walrus operator" will occasionally be useful, but I doubt I will find many effective uses for it. The primary one I want is if m := re.match(...): print(m.group(1)) and while s := network_service.read(): process(s) both of which are both clearer and less error-prone than their non-walrus variants. The other one that I would have found useful an hour ago is in interactive exploration with comprehensions. I freq…

IMHO the whole `re.match` is a design flaw in stdlib. re.match() should always return a match object, but instead .group(1) will return None. Then we can write one-liners easier without the walrus operator.

    >>> import re
    >>> pat = re.compile("(A+)|(B+)")
    >>> m = pat.search("HUBBLE")
    >>> m.group(1) is None
    True
    >>> m.group(2)
    'BB'
    >>> m.group(0)
    'BB'

Post by duckerude » Tue, Oct 15, 2019, 10:35 AM UTC

enriquto wrote: post #233

rolux wrote: post #224

Earlier quoted context omitted.

That would of course be an absolute disaster, given that any user input could easily leak internal state and/or break your program.

I meant for inline strings (i.e., typed by the programmer). This is an inoffensive change. The only possible ``accident'' is when the programmer wants to write "{x}" instead of the value of x. This is such and exceptional case that it may be best treated by forcing to escape the curly brackets. If anything, user-input strings must be treated as tainted whatever the case.

Post by eesmith » Tue, Oct 15, 2019, 10:44 AM UTC

enriquto wrote: post #233

rolux wrote: post #224

Earlier quoted context omitted.

That would of course be an absolute disaster, given that any user input could easily leak internal state and/or break your program.

I meant for inline strings (i.e., typed by the programmer). This is an inoffensive change. The only possible ``accident'' is when the programmer wants to write "{x}" instead of the value of x. This is such and exceptional case that it may be best treated by forcing to escape the curly brackets. If anything, user-input strings must be treated as tainted whatever the case.

   aifc.py: raise Error('marker {0!r} does not exist'.format(id))

    argparse.py: result = '{%s}' % ','.join(choice_strs)

    uuid.py: if re.fullmatch('(?:[0-9a-f][0-9a-f]-){5}[0-9a-f][0-9a-f]', value):

    uuid.py: >>> x = uuid.UUID('{00010203-0405-0607-0809-0a0b0c0d0e0f}')

Post by heavenlyblue » Tue, Oct 15, 2019, 10:50 AM UTC

bouncing wrote: post #249

Xophmeister wrote: post #241

This got missed from the release announcement, but now there's `functools.singledispatchmethod`,[1] as the class method sibling to `functools.singledispatch`.[2] This allows you to overload the implementation of a function (and now a method) based on the type of its first argument. This saves you writing code like: def foo(bar): if isinstance(bar, Quux): # Treat bar as a Quux elif isinstance(bar, Xyzzy): # Treat bar…

I can definitely imagine some places where this replaces type-checking, but it still seems like a bit of an unfortunate anti-pattern to me, since it's really a sort of C/C++ style function prototype match. My immediate thought is that it's going to be hard for PyCharm to reliably point me to a function definition.