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Python Regular Expressions in Python Introduction to Regular Expressions Word Length

Mona Jalal
Mona Jalal
4,302 Points
Posted by Mona Jalal
Mona Jalal
4,302 Points

returned []

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)

or

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)

both return [] why?

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)

2 Answers

Kourosh Raeen
Kourosh Raeen
23,733 Points
Kourosh Raeen
Kourosh Raeen
23,733 Points

Hi Mona - The problem is that count is inside quotes so the number passed into the function is not used. Try creating the pattern using string concatenation:

import re

# EXAMPLE:
# >>> find_words(4, "dog, cat, baby, balloon, me")
# ['baby', 'balloon']
def find_words(count, string):
    return re.findall(r'\w{' + str(count) + ',}', string)

Notice that I am casting count to a string. Also, notice the comma after count. That is needed since we want words that are count characters or longer. Without it you'd get those words that are exactly count characters long.

Unsubscribed User
Unsubscribed User
7,260 Points
Unsubscribed User
Unsubscribed User
7,260 Points

Hi Kourosh,

I'm in the same boat as Mona. I do not understand why we have to convert count to a string.. In the examples and the video we see that count is a number be it 1, 2, 3,... When they say count number of times, for me it means that count is the same as saying x-amount of times.

I don't understand at all why we are converting a number to a string to input it in the location where a number should be put..

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)
Kourosh Raeen
Kourosh Raeen
23,733 Points
Kourosh Raeen
Kourosh Raeen
23,733 Points

Hi Kevin - count is a variable but once you put it inside quotes, as in your code above, then python just treats that as part of that string so its value doesn't get substituted there. it's like the following code:

count = 5
print(count)
print('count')

The first print statement prints 5, but the second one just prints the string "count". So count should be outside the single quotes so that you can get its value. Now, why convert the number to a string? Because the whole pattern we are trying to match needs to be a string. Notice that in the videos the number that is used is inside the single quotes and part of the pattern to match, which is a string. So we need the value of the variable count but then we need to concatenate that to the other strings to create the pattern and if you don't convert that to a string python will complain.

Hope this makes sense.