Master Python Regex: Using s and S to Match Spaces and Non‑Spaces

Special Characters s and S in Python Regex

Continuing the series on Python regular expressions, this article focuses on the special characters s (matches any whitespace) and S (matches any non‑whitespace).

1. Using s to match a single space

The pattern 加 s 油 matches the string "加 油" because there is a space between the two Chinese characters.

2. No space – match fails

When the source string is changed to "加加油" (no space) while keeping the same pattern, the match fails, producing no output.

3. Matching multiple spaces with s+

To match one or more spaces, replace s with s+ in the pattern, e.g., 加 s+ 油. This succeeds when there are multiple spaces.

4. Using S to match any non‑space character

The character S matches any character except whitespace. Changing the pattern from 加 s 油 to 加 S 油 makes the match succeed on the string "加加油".

5. Non‑space match fails when a space is present

If the source string is "加 油" (contains a space) and the pattern uses S, the match fails because S does not match spaces.

6. Matching multiple non‑space characters with S+

To match a sequence of non‑space characters, use S+ in the pattern. This succeeds on strings like "加加油".

Understanding the difference between s and S helps you craft precise regular expressions for whitespace and non‑whitespace matching in Python.