Pattern Matching - Repetition Qualifiers

• affects the count to match from the preceding character or group
• Can have a variable or specific range

Repetition Qualifier Characters

• match 0 or more occurrences ? match 0 or 1 occurrence of the previous entity
• match 1 or more occurrences

Specific Repetition Qualifiers

{n}
# match exactly n occurrences
{n,}
# match at least n occurrences
{n,m}
# match between n and m occurrences
{,m}
# match between 0 and m occurrences

Repetition Example 1

• \d* match 0 or more consecutive digits

Pattern	String	result
\d*	(empty string)	match
\d*	8	match
\d*	1234	match
\d*	12345	match

Repetition Example 2

• \d? match 0 or one consecutive digit

Pattern	String	result
\d?	(empty string)	match
\d?	8	match
\d?	1234	match
\d?	12345	match

Repetition Example 3

• \d+ match 1 or more consecutive digit

Pattern	String	result
\d+	(empty string)	no match
\d+	8	match
\d+	1234	match
\d+	12345	match

Repetition Example 4

• \d{5} match any 5 consecutive digit

Pattern	String	result
\d{5}	(empty string)	no match
\d{5}	8	no match
\d{5}	1234	no match
\d{5}	12345	match

Repetition Example 5

• \d{1,4} match 1 to 4 consecutive digit

Pattern	String	result
\d{1,4}	(empty string)	match
\d{1,4}	8	match
\d{1,4}	1234	match
\d{1,4}	12345	match

Greedy Qualifiers

• Match as much text as possible (Greedy)
• Include all repetition qualifiers (*,+,?)
• may lead to unexpected results
• avoid using . together with greedy qualifiers (it matches pretyt much everything)

Greedy Example

import re

s = '<tag>data</tag>'
pattern = '<.*>'
match = re.search(pattern,s)
print(match.group(0))
# Output <tag>data</tag>

Handling Greedy Matching

• use alternaties to repetition qualifiers (to avoid greedy )
• to turn off greedy matching add the ? right after the qualifier (makes it non-greedy)
• Use specific or custom character classes instead of the dot (.)

Non-Greedy Matching

import re

s = '<tag>data</tag>'
pattern = '<.*?>'
match = re.search(pattern,s)
print(match.group(0))
# Output <tag>