8.6. Syntax Quantifier

  • Quantifier specifies how many occurrences of preceding qualifier or identifier

  • Exact

  • Greedy

  • Lazy

>>> import re
>>> TEXT = 'Mark Watney of Ares 3 landed on Mars on: Nov 7th, 2035 at 1:37 pm'

>>> re.findall(r'\d', TEXT)
['3', '7', '2', '0', '3', '5', '1', '3', '7']

>>> re.findall(r'\d\d\d\d', TEXT)
['2035']

8.6.1. Exact

  • Exact match

  • {n} - exactly n repetitions, prefer longer

>>> TEXT = 'Mark Watney of Ares 3 landed on Mars on: Nov 7th, 2035 at 1:37 pm'

>>> re.findall(r'[0-9]{2}', TEXT)
['20', '35', '37']

>>> re.findall(r'\d{2}', TEXT)
['20', '35', '37']

8.6.2. Greedy

  • Prefer longest matches

  • Works better with numbers

  • Not that good results for text

  • Default behavior

  • {,n} - maximum n repetitions, prefer longer

  • {n,} - minimum n repetitions, prefer longer

  • {n,m} - minimum n repetitions, maximum m times, prefer longer

  • * - minimum 0 repetitions, no maximum, prefer longer (alias to {0,})

  • + - minimum 1 repetitions, no maximum, prefer longer (alias to {1,})

  • ? - minimum 0 repetitions, maximum 1 repetitions, prefer longer (alias to {0,1})

>>> TEXT = 'Mark Watney of Ares 3 landed on Mars on: Nov 7th, 2035 at 1:37 pm'

>>> re.findall(r'\d{2,4}', TEXT)
['2035', '37']

8.6.3. Lazy

  • Prefer shortest matches

  • Works better with text

  • Not that good results for numbers

  • Non-greedy

  • {,n}? - maximum n repetitions, prefer shorter

  • {n,}? - minimum n repetitions, prefer shorter

  • {n,m}? - minimum n repetitions, maximum m times, prefer shorter

  • *? - minimum 0 repetitions, no maximum, prefer shorter (alias to {0,}?)

  • +? - minimum 1 repetitions, no maximum, prefer shorter (alias to {1,}?)

  • ?? - minimum 0 repetitions, maximum 1 repetition, prefer shorter (alias to {0,1}?)

>>> TEXT = 'Mark Watney of Ares 3 landed on Mars on: Nov 7th, 2035 at 1:37 pm'

>>> re.findall(r'\d{2,4}?', TEXT)
['20', '35', '37']

8.6.4. Greedy vs. Lazy

>>> TEXT = 'Mark Watney of Ares 3 landed on Mars on: Nov 7th, 2035 at 1:37 pm'

>>> re.findall(r'\d{2,4}', TEXT)  # Greedy
['2035', '37']

>>> re.findall(r'\d{2,4}?', TEXT)  # Lazy
['20', '35', '37']

Greedy vs Lazy in exact match has no difference:

>>> re.findall('\d{2}?', TEXT)
['20', '35', '37']

>>> re.findall('\d{2}', TEXT)
['20', '35', '37']

8.6.5. Special

>>> TEXT = 'Mark Watney of Ares 3 landed on Mars on: Nov 7th, 2035 at 1:37 pm'

>>> re.findall('\d{0,}', TEXT) == re.findall('\d*', TEXT)
True

>>> re.findall('\d{1,}', TEXT) == re.findall('\d+', TEXT)
True

>>> re.findall('\d+', TEXT)
['3', '7', '2035', '1', '37']

>>> re.findall('\d*', TEXT)  
['', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '',
 '', '', '3', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '',
 '', '', '', '', '', '', '', '', '', '7', '', '', '', '', '2035', '', '',
 '', '', '1', '', '37', '', '', '', '']

8.6.6. Examples

  • [0-9]{2} - exactly two digits from 0 to 9

  • \d{2} - exactly two digits from 0 to 9

  • [A-Z]{2,10} - two to ten uppercase letters from A to Z

  • [A-Z]{2-10}-[0-9]{,5} - two to ten uppercase letters from A to Z followed by dash (-) and at least five numbers

  • [a-z]+ - at least one lowercase letter from a to z, but try to fit the longest match

  • \d+ - number

  • \d+\.\d+ - float

8.6.7. Use Case - 0x01

  • Float

>>> import re
>>> TEXT = 'Pi number is 3.1415...'

>>> pi = re.findall('\d+\.\d+', TEXT)
>>> pi
['3.1415']

8.6.8. Use Case - 0x02

  • Time

>>> import re
>>> TEXT = 'Mark Watney of Ares 3 landed on Mars on: Nov 7th, 2035 at 1:37 pm'

>>> re.findall('\d\d:\d\d', TEXT)
[]

>>> re.findall('\d\d?:\d\d', TEXT)
['1:37']

8.6.9. Use Case - 0x03

  • Date

>>> import re
>>> from datetime import datetime

>>> TEXT = 'Mark Watney of Ares 3 landed on Mars on: Nov 7th, 2035 at 1:37 pm'
>>>
>>> result = re.findall('\w{3} \d{1,2}th, \d{4}', TEXT)

>>> result
['Nov 7th, 2035']

>>> datetime.strptime(result[0], '%b %dth, %Y').date()
datetime.date(2035, 11, 7)

8.6.10. Use Case - 0x04

>>> import re

>>> line = 'value=123'
>>>
>>> re.findall(r'(\w+)\s?=\s?(\d+)', line)
[('value', '123')]

>>> line = 'value = 123'
>>>
>>> re.findall(r'(\w+)\s?=\s?(\d+)', line)
[('value', '123')]

8.6.11. Use Case - 0x05

>>> import re
>>> HTML = '<h1>Header 1</h1><p>Paragraph 1</p><p>Paragraph 2</p>'

>>> re.findall('<p>.*</p>', HTML)
['<p>Paragraph 1</p><p>Paragraph 2</p>']

>>> re.findall('<p>.*?</p>', HTML)
['<p>Paragraph 1</p>', '<p>Paragraph 2</p>']

8.6.12. Use Case - 0x06

>>> import re
>>> HTML = '<h1>Header 1</h1><p>Paragraph 1</p><p>Paragraph 2</p>'

>>> re.findall('<p>', HTML)
['<p>', '<p>']

>>> re.findall('</p>', HTML)
['</p>', '</p>']

>>> re.findall('</?p>', HTML)
['<p>', '</p>', '<p>', '</p>']

8.6.13. Use Case - 0x07

>>> import re
>>> HTML = '<h1>Header 1</h1><p>Paragraph 1</p><p>Paragraph 2</p>'

>>> re.findall('<.+>', HTML)
['<h1>Header 1</h1><p>Paragraph 1</p><p>Paragraph 2</p>']

>>> re.findall('<.+?>', HTML)
['<h1>', '</h1>', '<p>', '</p>', '<p>', '</p>']

>>> re.findall('</?.+?>', HTML)
['<h1>', '</h1>', '<p>', '</p>', '<p>', '</p>']

>>> re.findall('</?(.+?)>', HTML)
['h1', 'h1', 'p', 'p', 'p', 'p']

>>> tags = re.findall('</?(.+?)>', HTML)
>>> sorted(set(tags))
['h1', 'p']

8.6.14. Use Case - 0x08

>>> import re
>>> HTML = '<h1>Header 1</h1><p>Paragraph 1</p><p>Paragraph 2</p>'

>>> re.findall('</?.*>', HTML)
['<h1>Header 1</h1><p>Paragraph 1</p><p>Paragraph 2</p>']

>>> re.findall('</?.*?>', HTML)
['<h1>', '</h1>', '<p>', '</p>', '<p>', '</p>']