assignment expression peeve

[Daniel Dittmar]

Paul Rubin wrote:
> OK, I want to scan a file for lines matching a certain regexp.  I'd
> like to use an assignment expression, like
>
>    for line in file:
>       if (g := re.match(pat, line)):
>          croggle(g.group(1))
[...]
> It gets annoying when there are 4 different regexps that the line
> might match, and I want to do something different depending on which
> one matches.  That's not that uncommon a text scanning situation.
> With assignment expressions, it's a very natural if/elif chain:
[...]
> This kind of regexp matching is a common pattern and I keep wanting
> assignment expressions whenever I code it, and end up crocking up some
> silly workaround.

If this is a common pattern in your code, then write an iterator class that
reads lines from a file and spits out the match object (+ tag, so you know
which regular expression was matched.
So your code becomes:

for match, tag in LineMatcher (...).parseFile (fname):
    if tag == tag1:
        action1
    elif tag == tag2:
        action2

cons: you have to invent names for every pattern
pros: patterns are compiled and thus more efficient

Daniel