Question

I’m a newbie in Python and I’m studying list comprehension.

What I’m trying to do is to convert the following code into list comprehension:

def words_without_e():
    count = 0

    words = open('words.txt')
    for word in words:
        if word.find('e') == -1:
            count += 1
    words.close()

    return count

Here’s my feeble attempt:

words = open('words.txt')
print sum([1 for word in words if word.find('e') == -1])

But unfortunately it’s not working. The answer I expect to get is 37641, but I’m getting 0. 🙁

I tried creating another code doing the same thing but instead of file as source, I used a list:

def test():
    words = ['hello', 'world', 'ciao']
    return sum([1 for word in words if word.find('e') == -1])

And it works.

I saw this “quite” similar SO post and tried the code posted there return len([word for word in words if len(word) >= 2 and word[0] == word[-1]]). It works if the source is a hard-coded list but fails if the source is an external file.

Now, my question is, does sum only works with lists and tuples? If I understood the docs correctly, any iterable could be summed up.

Any enlightenment would be very much appreciated. 🙂

Answer 1

The simplest solution is this:

with open("words.txt") as words:
  sum(1 for word in words if "e" not in word)

As you can see, sum does work with any iterator – here I am using a generator expression.

Rather than doing word.find('e') == -1 we can just do "e" not in word which is nicer to read and works as strings are iterable themselves and support __contains__.

I am also using the with statement to open files – this is preferable to manually opening and closing them as it handles those things for you, and handles exceptions correctly too.

I would like to note however, your example works for me. My guess is that your file is space or comma delimited, but looping through a file returns lines.

My test file:

bob
bill
james
test
something
no

This, for example, will not work:

bob bill james test something no

As we will get one string containing the whole thing. In this case, we can use str.split() to split the lines into words.

E.g:

with open("words.txt") as lines:
    sum(1 for line in lines for word in line.split() if "e" not in word)