Question 1

What re.findall returns

Accepted Answer

re.findall() returns a plain Python list of all non-overlapping matches as strings, not Match objects. The pattern r'\d+' matches one or more digit characters, so it finds '42', '3', and '100' in order. The return type is always a list of strings (or a list of tuples when the pattern contains capturing groups). Because the values come back as strings, you need int() or float() if you plan to do arithmetic on them.

Question 2

Raw strings in regex patterns

Accepted Answer

Python processes escape sequences in ordinary string literals before passing the string to the regex engine. '\d' is not a recognized Python escape, so Python leaves it as the two characters '\' and 'd' - which happens to work here. But '
' IS a Python escape (newline), so '
+' and r'
+' mean completely different things to the regex engine. The r prefix tells Python to treat every backslash literally, so what you type is exactly what the regex engine receives. Using raw strings eliminates an entire class of subtle bugs and makes patterns much easier to read.

Question 3

re.search vs re.match - key difference

Accepted Answer

re.match() anchors implicitly to the start of the string - if the pattern does not match at position 0 it returns None immediately, without looking further. re.search() scans forward through the string until it finds a position where the pattern matches, then returns that match. A practical consequence: re.match(r'\d+', 'abc123') returns None, but re.search(r'\d+', 'abc123') returns a match for '123'. For most production code, re.search() is the safer default. Use re.match() only when you specifically need to validate that the string starts with the pattern.

Question 4

re.match anchors to the start

Accepted Answer

re.match() tries to match at position 0 only. The string starts with 'h', not a digit, so it returns None immediately. re.search() scans the whole string and finds '42' at the end, returning a Match object whose .group() is '42'. This example is a clean demonstration of why using re.match() when you mean re.search() silently produces None instead of finding your data - a very common source of bugs in data parsing scripts.

Question 5

Raw string vs regular string in a pattern

Accepted Answer

Both patterns actually match the same thing here, but for different reasons. In the raw string r'
', the regex engine receives the two characters '\' and 'n' and interprets them as the newline meta-sequence. In the regular string '
', Python first converts 
 to an actual newline character (one char), and the regex engine then matches that literal newline. Both find the single newline in 'line1
line2', so both counts are 1. The output is '1 1'. The danger with regular strings shows up with patterns like '\b' (word boundary) - Python turns \b into a backspace character before the regex engine sees it, producing a completely wrong pattern.