Jen,
I had no doubt the code you ran was indented properly or it would not work.
I am merely letting you know that somewhere in the process of copying the code
or the transition between mailers, my version is messed up. It happens to be
easy for me to fix but I sometimes see garbled code I then simply ignore.
At times what may help is to leave blank lines that python ignores but also
keeps the line rearrangements minimal.
On to your real question.
In my OPINION, there are many interesting questions that can get in the way of
just getting a working solution. Some may be better in some abstract way but
except for big projects it often hardly matters.
So regex is one thing or more a cluster of things and a list comp is something
completely different. They are both tools you can use and abuse or lose.
The distinction I believe we started with was how to find a fixed string inside
another fixed string in as many places as needed and perhaps return offset
info. So this can be solved in too many ways using a side of python focused on
pure text. As discussed, solutions can include explicit loops such as “for” and
“while” and their syntactic sugar cousin of a list comp. Not mentioned yet are
other techniques like a recursive function that finds the first and passes on
the rest of the string to itself to find the rest, or various functional
programming techniques that may do sort of hidden loops. YOU DO NOT NEED ALL OF
THEM but it can be interesting to learn.
Regex is a completely different universe that is a bit more of MORE. If I ask
you for a ride to the grocery store, I might expect you to show up with a car
and not a James Bond vehicle that also is a boat, submarine, airplane, and
maybe spaceship. Well, Regex is the latter. And in your case, it is this
complexity that meant you had to convert your text so it will not see what it
considers commands or hints.
In normal use, put a bit too simply, it wants a carefully crafted pattern to be
spelled out and it weaves an often complex algorithm it then sort of compiles
that represents the understanding of what you asked for. The simplest pattern
is to match EXACTLY THIS. That is your case.
A more complex pattern may say to match Boston OR Chicago followed by any
amount of whitespace then a number of digits between 3 and 5 and then should
not be followed by something specific. Oh, and by the way, save selected parts
in parentheses to be accessed as \1 or \2 so I can ask you to do things like
match a word followed by itself. It goes on and on.
Be warned RE is implemented now all over the place including outside the usual
UNIX roots and there are somewhat different versions. For your need, it does
not matter.
The compiled monstrosity though can be fairly fast and might be a tad hard for
you to write by yourself as a bunch of if statements nested that are weirdly
matching various patterns with some look ahead or look behind.
What you are being told is that despite this being way more than you asked for,
it not only works but is fairly fast when doing the simple thing you asked for.
That may be why a text version you are looking for is hard to find.
I am not clear what exactly the rest of your project is about but my guess is
your first priority is completing it decently and not to try umpteen methods
and compare them. Not today. Of course if the working version is slow and you
profile it and find this part seems to be holding it back, it may be worth
examining.
From: Jen Kris <jenk...@tutanota.com>
Sent: Tuesday, February 28, 2023 12:58 PM
To: avi.e.gr...@gmail.com
Cc: 'Python List' <python-list@python.org>
Subject: RE: How to escape strings for re.finditer?
The code I sent is correct, and it runs here. Maybe you received it with a
carriage return removed, but on my copy after posting, it is correct:
example = 'X - abc_degree + 1 + qq + abc_degree + 1'
find_string = re.escape('abc_degree + 1')
for match in re.finditer(find_string, example):
print(match.start(), match.end())
One question: several people have made suggestions other than regex (not your
terser example with regex you shown below). Is there a reason why regex is not
preferred to, for example, a list comp? Performance? Reliability?
Feb 27, 2023, 18:16 by avi.e.gr...@gmail.com <mailto:avi.e.gr...@gmail.com> :
Jen,
Can you see what SOME OF US see as ASCII text? We can help you better if we get
code that can be copied and run as-is.
What you sent is not terse. It is wrong. It will not run on any python
interpreter because you somehow lost a carriage return and indent.
This is what you sent:
example = 'X - abc_degree + 1 + qq + abc_degree + 1'
find_string = re.escape('abc_degree + 1') for match in re.finditer(find_string,
example):
print(match.start(), match.end())
This is code indentedproperly:
example = 'X - abc_degree + 1 + qq + abc_degree + 1'
find_string = re.escape('abc_degree + 1')
for match in re.finditer(find_string, example):
print(match.start(), match.end())
Of course I am sure you wrote and ran code more like the latter version but
somewhere in your copy/paste process, ....
And, just for fun, since there is nothing wrong with your code, this minor
change is terser:
example = 'X - abc_degree + 1 + qq + abc_degree + 1'
for match in re.finditer(re.escape('abc_degree + 1') , example):
... print(match.start(), match.end())
...
...
4 18
26 40
But note once you use regular expressions, and not in your case, you might
match multiple things that are far from the same such as matching two repeated
words of any kind in any case including "and and" and "so so" or finding words
that have multiple doubled letter as in the stereotypical bookkeeper. In those
cases, you may want even more than offsets but also show the exact text that
matched or even show some characters before and/or after for context.
-----Original Message-----
From: Python-list <python-list-bounces+avi.e.gross=gmail....@python.org
<mailto:python-list-bounces+avi.e.gross=gmail....@python.org> > On Behalf Of
Jen Kris via Python-list
Sent: Monday, February 27, 2023 8:36 PM
To: Cameron Simpson <c...@cskk.id.au <mailto:c...@cskk.id.au> >
Cc: Python List <python-list@python.org <mailto:python-list@python.org> >
Subject: Re: How to escape strings for re.finditer?
I haven't tested it either but it looks like it would work. But for this case I
prefer the relative simplicity of:
example = 'X - abc_degree + 1 + qq + abc_degree + 1'
find_string = re.escape('abc_degree + 1') for match in re.finditer(find_string,
example):
print(match.start(), match.end())
4 18
26 40
I don't insist on terseness for its own sake, but it's cleaner this way.
Jen
Feb 27, 2023, 16:55 by c...@cskk.id.au <mailto:c...@cskk.id.au> :
On 28Feb2023 01:13, Jen Kris <jenk...@tutanota.com
<mailto:jenk...@tutanota.com> > wrote:
I went to the re module because the specified string may appear more than once
in the string (in the code I'm writing).
Sure, but writing a `finditer` for plain `str` is pretty easy (untested):
pos = 0
while True:
found = s.find(substring, pos)
if found < 0:
break
start = found
end = found + len(substring)
... do whatever with start and end ...
pos = end
Many people go straight to the `re` module whenever they're looking for
strings. It is often cryptic error prone overkill. Just something to keep in
mind.
Cheers,
Cameron Simpson <c...@cskk.id.au <mailto:c...@cskk.id.au> >
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