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Python Regular Expressions in Python Introduction to Regular Expressions Word Length

Alexander Lausten
Alexander Lausten
3,223 Points
Posted by Alexander Lausten
Alexander Lausten
3,223 Points

word_length.py better aproach?

Hi people ^_^

so i just completed the challenge of word_length.py however in not satisfied with how i ended up doing it and i havent been able to find a better aproach so i tougth it better to ask here! normally when passing a variable to a string we are tought to use .format

so i tried r'\d{}'.format(count) and that returned: r'\d5'

next i tried: r'\d{{}}'.format(count) that return r'\d{{}}'

you can see my solution to the problem in the code but i'd like to khow does anyone know of a better aproach to solve this than using + to glue together strings?

word_length.py 
import re

# EXAMPLE:
# >>> find_words(4, "dog, cat, baby, balloon, me")
# ['baby', 'balloon']

def find_words(count, string):
    return re.findall(r'\d{'+str(count)+',}', string)

2 Answers

Boris Ivan Barreto
Boris Ivan Barreto
6,838 Points
Boris Ivan Barreto
Boris Ivan Barreto
6,838 Points

If you wanna use str.format statement, you should use a triple square brackets, for instance if you wanna print {4}, you should use {{{0}}}.format(4). So we use this in the return statement as follow

          return re.findall(r'\w{{{0},}}'.format(count), string)
Mike Wagner
Mike Wagner
23,559 Points

+1 - I had forgotten about triple-bracing. Well done.

Lauren Gainsbrook
Lauren Gainsbrook
12,539 Points
Lauren Gainsbrook
Lauren Gainsbrook
12,539 Points

Hey! I understand how to solve this with formatting.... I just don't know why the third set of braces is needed?! Can you explain?

Mike Wagner
Mike Wagner
23,559 Points

Lauren Gainsbrook - I can't explain it as well as Boris Ivan Barreto probably will (since I had forgotten about it entirely) but the addition of the double braces on each side essentially tell it the string literally contains "\w{{0},}" which is almost exactly the same syntax as the old version formatting I showed in my answer. In this case, the {0} is your placeholder object for the .format() functionality.

Boris Ivan Barreto
Boris Ivan Barreto
6,838 Points
Boris Ivan Barreto
Boris Ivan Barreto
6,838 Points

This is a Python standard string formatting. The format string contain “replacement fields”, which is surrounded by curly braces {}, and anything that is not surrounded by braces is considered as literal text.

"My number: {0}".format(4)
>> My number: 4

However if you want to include the brace character in the literal text, you should escaped by doubling {{ }}.

"My number is {0} - {{Fine}}".format(4)
>> My number is 4 - {Fine}

Back to your question, we need to combine those two concepts in order to obtain the “replacement field” inside curly braces. {{{0}}}, so first two curly braces will print the braces character, and the {0} represents the “replacement field”

"My number is {{{0}}} ".format(4)
>> My number is {4}
"My number is {{{0}, some text}} ".format(4)
>> My number is {4, some text}

More information you can find in in the PEP 3101 -- Advanced String Formatting

Lauren Gainsbrook
Lauren Gainsbrook
12,539 Points
Lauren Gainsbrook
Lauren Gainsbrook
12,539 Points

Great explanation! Thank you so much!

Mike Wagner
Mike Wagner
23,559 Points
Mike Wagner
Mike Wagner
23,559 Points

It may not be the best idea, nor am I sure it's "better" per se, but you can also use the old formatting style % to carry on the format operation. Replacing

return re.findall(r'\d{'+str(count)+',}', string)

with

return re.findall(r'\w{%c,}' % (count), string)

will also yield a passing solution. This way also doesn't require count to be cast as a string, though you still can to be safe, if you wanted. I'm not sure that it's any more readable with mine than yours or vice versa, but I imagine there isn't much of a difference in performance either.

There might be a better alternative that I can't think of at the moment. I suppose if you wanted to, you could add in extra code and use a recompile call to avoid concatenating strings but, I think, that would probably just make things overly complicated and probably make take up time and energy from both the coder and the program itself. Essentially, it's not really all that bad to concat strings and, if the code is readable and easy to understand, it's probably the best way to do something so trivial.