[Python-Dev] Assignment expression and coding style: the while True case (original) (raw)

Victor Stinner vstinner at redhat.com
Wed Jul 4 20:03:23 EDT 2018

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On the 3360 for loops of the stdlib (*), I only found 2 loops which would benefit of assignment expressions.

It's not easy to find loops which:

• build a list,
• are simple enough to be expressed as list comprehension,
• use a condition (if),
• use an expression different than just a variable name as the list value (value appended to the list).

diff --git a/Lib/mailbox.py b/Lib/mailbox.py index 056251dce0..dc61a3a8b6 100644 --- a/Lib/mailbox.py +++ b/Lib/mailbox.py @@ -1341,9 +1341,9 @@ class Babyl(_singlefileMailbox): if len(stops) < len(starts): stops.append(line_pos - len(linesep)) starts.append(next_pos)

•            labels = [label.strip() for label

•                                    in

self._file.readline()[1:].split(b',')

•                                    if label.strip()]

•            labels = [slabel for label

•                      in self._file.readline()[1:].split(b',')

•                      if (slabel := label.strip())]
             label_lists.append(labels)
         elif line == b'\037' or line == b'\037' + linesep:
             if len(stops) < len(starts):

diff --git a/Lib/nntplib.py b/Lib/nntplib.py index 5961a28ab7..a5d13e35be 100644 --- a/Lib/nntplib.py +++ b/Lib/nntplib.py @@ -843,11 +843,9 @@ class _NNTPBase: DeprecationWarning, 2) line_pat = re.compile('^([^ \t]+)[ \t]+(.*)$') resp, raw_lines = self._longcmdstring('XGTITLE ' + group, file)

•    lines = []

•    for raw_line in raw_lines:

•        match = line_pat.search(raw_line.strip())

•        if match:

•            lines.append(match.group(1, 2))

•    lines = [match.group(1, 2)

•             for raw_line in raw_lines

•             if (match := line_pat.search(raw_line.strip()))]
     return resp, lines

  def xpath(self, id):

(*) Command used to count the number of for loops in the stdlib:

$ grep '\bfor\b' Lib/py Lib/{asyncio,logging,multiprocessing}/.py|grep -v '"""'|grep -v "'''"|grep -v '.py: *#'|wc -l 3360

Victor

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