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Python Regular Expressions in Python Introduction to Regular Expressions Word Length

Why can't I use a variable for count?

After testing this out in the shell, I have discovered that if I search for r"/w{4,}" it works perfectly. However, if I instead search for r"/w{some_variable,}" it returns nothing, even when some_variable has the value of 4.

Why does this happen and how do I fix this?

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"/w{count,}", string)

6 Answers

I got this working by converting the count integer to a string then concatenating that into the re.

def find_words(count, string):
    count = str(count)
    return re.findall(r"\w{"+count+",}", string)

With interpolation, I tried but was unable to figure out the solution:

def find_words(count, string):
    count = str(count)
    return re.findall(r"\w{{count},}", string)
# doesn't work

Steve.

I managed to got it to work by using

regex = r'\w{{{c},}}'.format(c=count)

But I got this from asking on Stack Exchange and still don't really know why this is necessary here.

Looks like the concatenation is an easier way to maintain clarity. All those braces don't add readability. I did try with one set of nested braces; I have no idea what the requirement for a two-deep nest is, though.

At least it is possible if not recommended!

Good work! :+1:

Hi Julian,

Did you try moving the comma?:

return re.findall(r"/w{count,}", string)

# try:

return re.findall(r"/w{count},", string)

Steve.

Didn't work. :wink:

Count isn't a string! Bear with me ...

The only thing I can think of is that maybe I need to use the actual value instead of a variable which is technically the memory address (i think?), but I also feel like python does that automatically so I have no idea why this doesn't work.

I'm trying all sorts ... my latest fail:

def find_words(count, string):
    count = str(count)
    return re.findall(r"\w{{},}".format(count), string)

This might assist ...

Looks like concatenation is required, as in the answer below; not interpolation.

Jimmy Smutek
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Jimmy Smutek
Python Web Development Techdegree Student 6,629 Points

I ran into the same problem and it's pretty frustrating because this scenario isn't covered in any of the preceding videos.

I don't mind trying to figure out additional things, but Regex is arcane and confusing enough as it is, and I would have expected this to have been covered in the lead up videos.

All told, between trying different regex patterns and rewatching the videos to see what I might have missed, I spent about an hour on this problem. It's just an unnecessary waste of time.

I see your point but I don't think regex can be reasonably called arcane. It is well used and documented. I'd also say that something that makes you research outside of the course materials for an hour is teaching you way more than just watching the videos alone. I bet you're way more familar with regex than you were previosuly and much of that learning wasn't from the videos. That's a good thing in many ways.

Just my thoughts. I neither speak for Treehouse nor understand regex particularly well!

Steve.

Jimmy Smutek
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.a{fill-rule:evenodd;}techdegree
Jimmy Smutek
Python Web Development Techdegree Student 6,629 Points

Okay, I'll concede that arcane wasn't the best word choice, and I'm definitely more familiar with regex at this point - but that is because of the material that's being taught in the videos and the exercises.

Sure, converting my integer to a string and concatenating it makes sense now, on the surface, but the point of the instruction at this stage is to learn how the sequences, characters and patterns work - at least that was what I was focused on.

I do understand your point. I spend a lot of time learning on my own, but unfortunately I didn't find that hour to be at all beneficial. It wasn't the good kind of research. It seems more like an oversight on the part of Treehouse, to be honest.

In fairness, I've not done these courses so can't really comment on their content. If you felt wholly unguided by the course videos then that's not ideal, obviously. Everyone learns differently, I guess - Treehouse has a narrow path to tread to meet everyone's needs.

Stick with it; you're clearly picking up lots so it isn't all fruitless.

Jimmy Smutek
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.a{fill-rule:evenodd;}techdegree
Jimmy Smutek
Python Web Development Techdegree Student 6,629 Points

:)

I'm getting older and can be cranky sometimes, but it's all good, and to clarify - despite some frustrations I can honestly say I do not regret having invested the time and money in this Tech Degree program. I'm learning tons, and Treehouse does a fantastic job, all told.

Thanks for the kind words.

I may try a Techdegree at some point. I have other certifications to chase first, though. Best of luck with it - I hope you get what you want from it.

Oh, I'm old and cranky all the time. And why not! :smile: :wink:

Steve.