Practical — Tags, Quotes, Numbers

Three real patterns combining everything

You now have quantifiers, character classes, anchors, and groups. Here's how they combine in real code.

HTML/XML tag (loose)

To extract simple tags like <div>, <p class="foo">: <[^>]+>. The negated class avoids the greedy .* trap. (Real HTML parsing still needs a parser — this works for ad-hoc extraction.)

Quoted string

Match anything between double quotes: "[^"]*". The negated class makes it ReDoS-safe and stops at the first closing quote. To handle escaped quotes inside (\"), the pattern grows: "(?:[^"\\]|\\.)*" — "non-quote-non-backslash, OR an escaped anything."

Number (integer or decimal, signed or unsigned)

-?\d+(\.\d+)? matches: optional minus, one or more digits, optional decimal portion. The decimal portion is wrapped in a group with ? to make the entire .\d+ sequence optional, not just the digits.

The quantifier checklist

When writing a real pattern with quantifiers, ask:

Is each piece + (required) or * (optional)?
Are my .* uses justified, or should they be [^X]*?
Are my {n,m} bounds tight (no whitespace inside)?
Did I anchor where appropriate (\b or ^...$)?
Did I test against empty input and very long input?

Five questions. They catch 90% of quantifier bugs.

Code

Three production-ready patterns·python

import re

# Loose HTML tag
re.findall(r'<[^>]+>', '<p>hi</p> <a href="x">link</a>')
# ['<p>', '</p>', '<a href="x">', '</a>']

# Quoted string with escape support
pat = r'"(?:[^"\\]|\\.)*"'
re.findall(pat, '"simple" "with \\"escape\\" inside"')
# ['"simple"', '"with \\"escape\\" inside"']

# Number: signed integer or decimal
for m in re.finditer(r'-?\d+(?:\.\d+)?', 'price -19.95 qty 7 ratio 0.5'):
    print(m.group())
# -19.95
# 7
# 0.5

Practical — Tags, Quotes, Numbers

Three real patterns combining everything

HTML/XML tag (loose)

Quoted string

Number (integer or decimal, signed or unsigned)

The quantifier checklist

Code

External links

Exercise

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