Outputting the line number of a text in a .txt-file, which doesn´t include spaces with list-comprehension

Question

I have a question reagarding my code, if anybody has some clues how to solve it. I need to write only one line of code, which outputs the line numbers of those lines that don´t include spaces between the words. My attempt was the following:

[line for line in range(len(open('test.txt').readlines())) if ' ' not in open('test.txt').readlines(line)]

I tried to use enumerate. But it didn`t work out as I intended. I would appreciate any clue on how to change my code, if anything of my code is correct.

Answer 1

The first step is to write your loop as a regular loop, then compress it into a list comprehension. What you have is:

lines = []

for line in range(len(open('test.txt').readlines()):
    if ' ' not in open('test.txt').readlines(line):
        lines.append(line)

Opening the file twice and using readlines() is rarely the right way to solve a problem. Instead, it's usually better to iterate over each line, one at a time.

The wonderful enumerate() function is a great way to get the index of elements as you iterate over them. It returns a tuple of (index, value) for each input of a list, or other iterable.

With it, your loop can become something like this:

for num, line in enumerate(open('test.txt')):
    if ' ' not in line:
        lines.append(num)

Converting the loop into a list comprehension is left as an exercise for you.

Answer 2

This does it:

print([i for i,line in (enumerate(open("test.txt").readlines())) if " " not in line])

Content of example file:

apricot
a p p l e
mango
banana
che rry

Output:

[0, 2, 3]