您如何将这种正则表达式习语从Perl转换为Python? [英] How do you translate this regular-expression idiom from Perl into Python?

问题描述

大约一年前，我从Perl切换到Python，并且没有回头.我发现只有一个 习惯用法在Perl中比在Python中更容易做:

I switched from Perl to Python about a year ago and haven't looked back. There is only one idiom that I've ever found I can do more easily in Perl than in Python:

if ($var =~ /foo(.+)/) {
  # do something with $1
} elsif ($var =~ /bar(.+)/) {
  # do something with $1
} elsif ($var =~ /baz(.+)/) {
  # do something with $1
}

由于if语句不断嵌套，因此相应的Python代码不太优雅:

The corresponding Python code is not so elegant since the if statements keep getting nested:

m = re.search(r'foo(.+)', var)
if m:
  # do something with m.group(1)
else:
  m = re.search(r'bar(.+)', var)
  if m:
    # do something with m.group(1)
  else:
    m = re.search(r'baz(.+)', var)
    if m:
      # do something with m.group(2)

有人能用优雅的方法在Python中重现此模式吗?我已经看到使用了匿名函数调度表，但是对于少量的正则表达式来说，这些表对于我来说似乎有点笨拙……

Does anyone have an elegant way to reproduce this pattern in Python? I've seen anonymous function dispatch tables used, but those seem kind of unwieldy to me for a small number of regular expressions...

推荐答案

从Python 3.8开始，并引入赋值表达式(PEP 572)(:=运算符)，我们现在可以在变量match中捕获条件值re.search(pattern, text)，以便检查它们是否不是然后在条件主体内重新使用它:

Starting Python 3.8, and the introduction of assignment expressions (PEP 572) (:= operator), we can now capture the condition value re.search(pattern, text) in a variable match in order to both check if it's not None and then re-use it within the body of the condition:

if match := re.search(r'foo(.+)', text):
  # do something with match.group(1)
elif match := re.search(r'bar(.+)', text):
  # do something with match.group(1)
elif match := re.search(r'baz(.+)', text)
  # do something with match.group(1)

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