{"id":356,"date":"2024-01-28T11:43:42","date_gmt":"2024-01-28T11:43:42","guid":{"rendered":"https:\/\/learnpython.elegantwallp.com\/?p=356"},"modified":"2024-01-28T11:43:46","modified_gmt":"2024-01-28T11:43:46","slug":"python-regex-capturing-group","status":"publish","type":"post","link":"https:\/\/learnpython.elegantwallp.com\/2024\/01\/28\/python-regex-capturing-group\/","title":{"rendered":"Python Regex Capturing Group"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you\u2019ll learn about Python regex capturing groups to create subgroups for a match.<\/p>\n\n\n\n

Introduction to the Python regex capturing groups<\/h2>\n\n\n\n

Suppose you have the following path that shows the news with the id 100 on a website:<\/p>\n\n\n\n

news\/100<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
The following\u00a0regular expression\u00a0matches the above path:<\/p>\n\n\n\n
\\w+\/\\d+<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
Note that the above regular expression also matches any path that starts with one or more word characters, e.g., posts<\/code>, todos<\/code>, etc. not just news<\/code>.<\/p>\n\n\n\n
In this pattern:<\/p>\n\n\n\n
    \n
  • \\w+<\/code>\u00a0is a word\u00a0character set\u00a0with a\u00a0quantifier\u00a0(+) that matches one or more word characters.<\/li>\n\n\n\n
  • \/<\/code> mathes the forward slash \/<\/code> character.<\/li>\n\n\n\n
  • \\d+<\/code> is digit character set with a quantfifer (+<\/code>) that matches one or more digits.<\/li>\n<\/ul>\n\n\n\n
    The following program uses the \\w+\/\\d+ pattern to match the string \u2018news\/100'<\/code>:<\/p>\n\n\n\n
    import re s = 'news\/100' pattern = '\\w+\/\\d+' matches = re.finditer(pattern,s) for match in matches: print(match)<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
    Output:<\/p>\n\n\n\n
    <re.Match object; span=(0, 8), match='news\/100'><\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
    It shows one match as expected.<\/p>\n\n\n\n
    To get the\u00a0id<\/code>\u00a0from the path, you use a capturing group. To define a capturing group for a pattern, you place the rule in parentheses:<\/code><\/p>\n\n\n\n
    (rule)<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
    For example, to create a capturing group that captures the\u00a0id<\/code>\u00a0from the path, you use the following pattern:<\/p>\n\n\n\n
    '\\w+\/(\\d+)'<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
    In this pattern, we place the rule\u00a0\\d+<\/code>\u00a0inside the parentheses\u00a0()<\/code>. If you run the program with the new pattern, you\u2019ll see that it displays one match:<\/p>\n\n\n\n
    import re s = 'news\/100' pattern = '\\w+\/(\\d+)' matches = re.finditer(pattern, s) for match in matches: print(match)<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
    Output:<\/p>\n\n\n\n
    <re.Match object; span=(0, 8), match='news\/100'><\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
    To get the capturing groups from a match, you the\u00a0group()<\/code>\u00a0method of the\u00a0Match<\/code>\u00a0object:<\/p>\n\n\n\n
    match.group(index)<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
    The group(0)<\/code> will return the entire match while the group(1)<\/code>, group(2)<\/code>, etc., return the first, second, \u2026 group.<\/p>\n\n\n\n
    The\u00a0lastindex<\/code>\u00a0property of the\u00a0Match<\/code>\u00a0object returns the last index of all subgroups. The following program shows the entire match (group(0)<\/code>) and all the subgroups:<\/p>\n\n\n\n
    import re s = 'news\/100' pattern = '\\w+\/(\\d+)' matches = re.finditer(pattern, s) for match in matches: for index in range(0, match.lastindex + 1): print(match.group(index))<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
    Output:<\/p>\n\n\n\n
    news\/100 100<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
    In the output, the news\/100<\/code> is the entire match while 100<\/code> is the subgroup.<\/p>\n\n\n\n
    If you want to capture also the resource (news<\/code>) in the path (news\/100<\/code>), you can create an additional capturing group like this:<\/p>\n\n\n\n
    '(\\w+)\/(\\d+)'<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
    In this pattern, we have two capturing groups one for\u00a0\\w+<\/code>\u00a0and the other for\u00a0\\d+<\/code>\u00a0. The following program shows the entire match and all the subgroups:<\/p>\n\n\n\n
    import re s = 'news\/100' pattern = '(\\w+)\/(\\d+)' matches = re.finditer(pattern, s) for match in matches: for index in range(0, match.lastindex + 1): print(match.group(index))<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
    Output:<\/p>\n\n\n\n
    news\/100 news 100<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
    In the output, the news\/100<\/code> is the entire match while news<\/code> and 100<\/code> are the subgroups.<\/p>\n\n\n\n
    Named capturing groups<\/h2>\n\n\n\n
    By default, you can access a subgroup in a match using an index, for example, match.group(1)<\/code>. Sometimes, accessing a subgroup by a meaningful name is more convenient.<\/p>\n\n\n\n
    You use the named capturing group to assign a name to a group. The following shows the syntax for assigning a name to a capturing group:<\/p>\n\n\n\n
    (?P<name>rule)<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
    In this syntax:<\/p>\n\n\n\n
      \n
    • ()<\/code> indicates a capturing group.<\/li>\n\n\n\n
    • ?P<name><\/code> specifies the name of the capturing group.<\/li>\n\n\n\n
    • rule<\/code> is a rule in the pattern.<\/li>\n<\/ul>\n\n\n\n
      For example, the following creates the names:<\/p>\n\n\n\n
      '(?P<resource>\\w+)\/(?P<id>\\d+)'<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
      In this syntax, the resource<\/code> is the name for the first capturing group and the id<\/code> is the name for the second capturing group.<\/p>\n\n\n\n
      To get all the named subgroups of a match, you use the\u00a0groupdict()<\/code>\u00a0method of the\u00a0Match<\/code>\u00a0object. For example:<\/p>\n\n\n\n
      import re s = 'news\/100' pattern = '(?P<resource>\\w+)\/(?P<id>\\d+)' matches = re.finditer(pattern, s) for match in matches: print(match.groupdict())<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
      Output:<\/p>\n\n\n\n
      {'resource': 'news', 'id': '100'}<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
      In this example, the groupdict()<\/code> method returns a dictionary where the keys are group names and values are the subgroups.<\/p>\n\n\n\n
      More named capturing group example<\/h3>\n\n\n\n
      The following pattern:<\/p>\n\n\n\n
      \\w+\/d{4}\/d{2}\/d{2}<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
      matches this path:<\/p>\n\n\n\n
      news\/2021\/12\/31<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
      And you can add the named capturing groups to the pattern like this:<\/p>\n\n\n\n
      '(?P<resource>\\w+)\/(?P<year>\\d{4})\/(?P<month>\\d{1,2})\/(?P<day>\\d{1,2})'<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
      This program uses the patterns to match the path and shows all the subgroups:<\/p>\n\n\n\n
      import re s = 'news\/2021\/12\/31' pattern = '(?P<resource>\\w+)\/(?P<year>\\d{4})\/(?P<month>\\d{1,2})\/(?P<day>\\d{1,2})' matches = re.finditer(pattern, s) for match in matches: print(match.groupdict())<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
      Output:<\/p>\n\n\n\n
      {'resource': 'news', 'year': '2021', 'month': '12', 'day': '31'}<\/code><\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"
      Summary: in this tutorial, you\u2019ll learn about Python regex capturing groups to create subgroups for a match. Introduction to the Python regex capturing groups Suppose you have the following path that shows the news with the id 100 on a website: The following\u00a0regular expression\u00a0matches the above path: Note that the above regular expression also matches […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[42],"tags":[],"class_list":["post-356","post","type-post","status-publish","format-standard","hentry","category-2-python-regex"],"_links":{"self":[{"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/posts\/356","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/comments?post=356"}],"version-history":[{"count":1,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/posts\/356\/revisions"}],"predecessor-version":[{"id":357,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/posts\/356\/revisions\/357"}],"wp:attachment":[{"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/media?parent=356"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/categories?post=356"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/tags?post=356"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}