Post History

First of all, let's understand why your regex didn't work.

The first part is `\w+\.\s`, which is "one or more alpha-numeric characters" (`\w+`), followed by a dot and a space (`\.\s`). If the regex was only this, it would *match* `THIS. `  (the word "THIS", plus the dot and space after it).

But you also used the [*lookahead*](https://www.regular-expressions.info/lookaround.html) `(?=[\.\s])`, which means that after `\w+\.\s` there **must** be another character, and that character must be a dot or a space. But after `THIS. `   there's a letter "T", so the *lookahead* fails in this case, thus no match is found.

It also can't find a match after "THAT", because it's followed by two dots (but the regex is looking for one dot and one space). And after "OTHER", there are no dots, only spaces, so the regex can't find any matches in this string.

---
Not entirely clear what parts of the string you want, but anyway...

If you want the words that are followed by a dot, you could do this:

```
import re

lines = [ 'THIS. THAT..OTHER                  ' ]

pattern = re.compile(r'\w+\.')
for line in lines:
    matches = pattern.findall(line)
    if matches:
        print(matches) # ['THIS.', 'THAT.']
    else:
        print("REGEX FAILED: [{}]".format(line))
```

`findall` returns a list containing all the matches found. In this case, I'm searching for `\w+\.` (one or more alphanumeric characters followed by a dot). The result is the list `['THIS.', 'THAT.']`.

But if you want a single string containing both words, then you could do:

```
pattern = re.compile(r'(\w+\.\s?)+')
for line in lines:
    match = pattern.search(line)
    if match:
        print(match[0]) # THIS. THAT.
    else:
        print("REGEX FAILED: [{}]".format(line))
```

Now I'm searching for `\w+\.` (alphanumeric characters followed by a dot), followed by an [optional](http://regular-expressions.info/optional.html) space (`\s?`). And  this whole thing (the word, dot and optional space) can be [repeated one or more times](https://www.regular-expressions.info/repeat.html) (this is indicated by the `+` in the end, which is applied to everything inside the parenthesis).

This finds the string `'THIS. THAT.'` (obtained from the `Match` object returned by the `search` method).

---
Not sure if this will work for all your cases (as you didn't specify all of them, I'm just assuming it's a "word, dot, space, word, dot" sequence), but anyway, you can make some adjustments according to your specific needs.

If you want to get the words from the beggining, [you can use `match` instead of `search`](https://docs.python.org/3/library/re.html#search-vs-match). Or, you can also make it explicit in the expression, by using the [anchor](https://www.regular-expressions.info/anchors.html) `^` (which indicates the beginning of the string):

```
pattern = re.compile(r'^(\w+\.\s?)+')
```

If you want to limit to only 2 words, just change the `+` quantifier:

```
pattern = re.compile(r'^(\w+\.\s?){2}')
```

You can customize the quantity in many different ways:

- `{2}`: exactly two ocurrences
- `{2,}`: two or more ocurrences (no upper limit)
- `{2,5}`: at least two, at most five ocurrences


---
Another caveat: in Python 3, the `\w` shorthand matches letters (from all languages, not only ASCII letters), digits (not restricted to arabic digits, so it'll also match characteres like `३` - [DEVANAGARI DIGIT THREE](https://www.fileformat.info/info/unicode/char/0969/index.htm)) and the character `_`. If you want to restrict to ASCII letters only, you could change it to:

```
pattern = re.compile(r'([a-zA-Z]+\.\s?)+')
```

And so on... the possibilities are endless, and the correct one(s) will depend on the data you have and what exactly you're trying to extract from it.