python re.compile strings with vars and numbers

Hi I want to get a match for the following:

test = re.compile(r开发者_JAVA百科' [0-12](am|pm) [1-1000] days from (yesterday|today|tomorrow)')

with this match:

print test.match(" 3pm 2 days from today")

It returns none, what am i doing wrong? I am just getting into regex and reading the docs I thought this should work! ANY HELP APPRECIATED chrism

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I am asking a new question about the design of a sytem using similar process to above in NLP HERE

Here is my hat in the ring. Careful study of this regex will teach a few lessons:

import re
reobj = re.compile(
    r"""# Loosely match a date/time reference
    ^                    # Anchor to start of string.
    \s*                  # Optional leading whitespace.
    (?P<time>            # $time: military or AM/PM time.
      (?:                # Group for military hours options.
        [2][0-3]         # Hour is either 20, 21, 22, 23,
      | [01]?[0-9]       # or 0-9, 00-09 or 10-19
      )                  # End group of military hours options.
      (?:                # Group for optional minutes.
        :                # Hours and minutes separated by ":"
        [0-5][0-9]       # 00-59 minutes
      )?                 # Military minutes are optional.
    |                    # or time is given in AM/PM format.
      (?:1[0-2]|0?[1-9]) # 1-12 or 01-12 AM/PM options (hour)
      (?::[0-5][0-9])?   # Optional minutes for AM/PM time.
      \s*                # Optional whitespace before AM/PM.
      [ap]m              # Required AM or PM (case insensitive)
    )                    # End group of time options.
    \s+                  # Required whitespace.
    (?P<offset> \d+ )    # $offset: count of time increments.
    \s+                  # Required whitespace.
    (?P<units>           # $units: units of time increment.
      (?:sec(?:ond)?|min(ute)?|hour|day|week|month|year|decade|century)
      s?                 # Time units may have optional plural "s".
    )                    # End $units: units of time increment.
    \s+                  # Required whitespace.
    (?P<dir>from|before|after|since) # #dir: Time offset direction.
    \s+                  # Required whitespace.
    (?P<base>yesterday|today|tomorrow|(?:right )?now)
    \s*                  # Optional whitespace before end.
    $                    # Anchor to end of string.""", 
    re.IGNORECASE | re.VERBOSE)
match = reobj.match(' 3 pm 2 days from today')
if match:
    print('Time:       %s' % (match.group('time')))
    print('Offset:     %s' % (match.group('offset')))
    print('Units:      %s' % (match.group('units')))
    print('Direction:  %s' % (match.group('dir')))
    print('Base time:  %s' % (match.group('base')))
else:
    print("No match.")

Output:

r"""
Time:       3 pm
Offset:     2
Units:      days
Direction:  from
Base time:  today
"""

This regex illustrates a few lessons to be learned:

• Regular expressions are very powerful (and useful)!
• This regex does validate the numbers, but as you can see, doing so is cumbersome and difficult (and thus, not recommended - I'm showing it here to demonstrate why not to do it this way). It is much easier to simply capture the numbers with a regex then validate the ranges using procedural code.
• Named capture groups ease the pain of plucking multiple data sub-strings from larger text.
• Always write regexes using free-spacing, verbose mode with proper indentation of groups and lots of descriptive comments. This helps while writing the regex and later during maintenance.

Modern regular expressions comprise a rich and powerful language. Once you learn the syntax and develop a habit of writing verbose, properly indented, well-commented code, then even complex regexes such as the one above are easy to write, easy to read and are easy to maintain. It is unfortunate that they have acquired a reputation for being difficult, unwieldy and error-prone (and thus not recommendable for complex tasks).

Happy regexing!

what about

test = re.compile(r' ([0-9]|1[012])(am|pm) \d+ days from (yesterday|today|tomorrow)')

the hours part should match 0, 1, ..., 9 or 10, 11, 12 but not 13, 14, ..., 19.

you can limit days part in similar way for 1, ..., 1000, i.e. (1000|\d{1,3}).

Try this:

test = re.compile(' \d+(am|pm) \d+ days from (yesterday|today|tomorrow)')

Try this:

import re

test = re.compile('^\s[0-1]?[0-9]{1}pm \d+ days from (today|yesterday|tomorrow)$')

print test.match(" 12pm 2 days from today")

The problem that you're having is that you can't specify multiple digit numeric ranges in regex (afaik), so you have to treat them as individual characters.

Sample here

If you want to extract the parts of the match individually, you can label the groups with (?P<name>[match]). For example:

import re

pattern = re.compile(
    r'\s*(?P<time>1?[0-9])(?P<ampm>am|pm)\s+'
    r'(?P<days>[1-9]\d*)\s+days\s+from\s+'
    r'(?P<when>yesterday|today|tomorrow)\s*')

for time in range(0, 13):
    for ampm in ('am', 'pm'):
        for days in range(1, 1000):
            for when in ('yesterday', 'today', 'tomorrow'):
                text = ' %d%s %d days from %s ' % (time, ampm, days, when)
                match = pattern.match(text)
                assert match is not None
                keys = sorted(match.groupdict().keys())
                assert keys == ['ampm', 'days', 'time', 'when']

text = ' 3pm 2 days from today '
print pattern.match(text).groupdict()

Output:

{'time': '3', 'when': 'today', 'days': '2', 'ampm': 'pm'}

test = re.compile(' 1?\d[ap]m \d{1,3} days? from (?:yesterday|today|tomorrow)')

EDIT

Having read the discussion between Rumple Stiltskin and Demian Brecht, I noticed that my above proposition is poor because it detects a certain structure of string, but it doesn't validate precisely it is a good "time-pattern" string, because it can detect " 18pm 2 days from today" for exemple.

So I propose now a pattern that allows to detect precisely a string verifying your requirement and that points out every string having the same structure as a valid one but not with the required values of a valid good "time-pattern" string:

import re

regx = re.compile("(?<= )"  # better than a blank as first character
                  ""
                  "(?:(1[012]|\d)([ap]m) (?!0 )(\d{1,3}|1000)"
                  "|"
                  "(\d+)([ap]m) (\d+))"
                  ""
                  " days? from (yesterday|today|tomorrow)") # shared part




for ch in (" 12pm 2 days from today",
           " 4pm 1 day from today",
           " 12pm 0 days from today",
           " 12pm 1001 days from today",
           " 18pm 2 days from today",
           " 1212pm 2 days from today",
           " 12pm five days from today"):

    print ch
    mat = regx.search(ch)
    if mat:
        if mat.group(1):
            print mat.group(1,2,3,7),'\n# time-pattern-VALIDATED string #'
        else:
            print mat.group(4,5,6,7),'\n* SIMILI-time-pattern STRUCTURED string*'
    else:
        print '- NO STRUCTURED STRING in the text -'
    print

result

 12pm 2 days from today
('12', 'pm', '2', 'today') 
# time-pattern-VALIDATED string #

 4pm 1 day from today
('4', 'pm', '1', 'today') 
# time-pattern-VALIDATED string #

 12pm 0 days from today
('12', 'pm', '0', 'today') 
* SIMILI-time-pattern STRUCTURED string*

 12pm 1001 days from today
('12', 'pm', '1001', 'today') 
* SIMILI-time-pattern STRUCTURED string*

 18pm 2 days from today
('18', 'pm', '2', 'today') 
* SIMILI-time-pattern STRUCTURED string*

 1212pm 2 days from today
('1212', 'pm', '2', 'today') 
* SIMILI-time-pattern STRUCTURED string*

 12pm five days from today
- NO STRUCTURED STRING in the text -

If you need only a regex that detects a time-pattern validated string, you use only

regx = re.compile("(?<= )(1[012]|\d)([ap]m) (?!0 )(\d{1,3}|1000) days?"
                  " from (yesterday|today|tomorrow)")

It is easier (and more readable) to check integer ranges after the match:

m = re.match(r' (\d+)(?:pm|am) (\d+) days from (yesterday|today|tomorrow)',
             " 3pm 2 days from today")
assert m and int(m.group(1)) <= 12 and 1 <= int(m.group(2)) <= 1000

Or you could use an existing library e.g., pip install parsedatetime:

import parsedatetime.parsedatetime as pdt

cal = pdt.Calendar()
print cal.parse("3pm 2 days from today")

Output

((2011, 4, 26, 15, 0, 0, 1, 116, -1), 3)