Regular Expressions 101

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An explanation of your regex will be automatically generated as you type.
Detailed match information will be displayed here automatically.
  • All Tokens
  • Common Tokens
  • General Tokens
  • Anchors
  • Meta Sequences
  • Quantifiers
  • Group Constructs
  • Character Classes
  • Flags/Modifiers
  • Substitution
  • A single character of: a, b or c
    [abc]
  • A character except: a, b or c
    [^abc]
  • A character in the range: a-z
    [a-z]
  • A character not in the range: a-z
    [^a-z]
  • A character in the range: a-z or A-Z
    [a-zA-Z]
  • Any single character
    .
  • Alternate - match either a or b
    a|b
  • Any whitespace character
    \s
  • Any non-whitespace character
    \S
  • Any digit
    \d
  • Any non-digit
    \D
  • Any word character
    \w
  • Any non-word character
    \W
  • Non-capturing group
    (?:...)
  • Capturing group
    (...)
  • Zero or one of a
    a?
  • Zero or more of a
    a*
  • One or more of a
    a+
  • Exactly 3 of a
    a{3}
  • 3 or more of a
    a{3,}
  • Between 3 and 6 of a
    a{3,6}
  • Start of string
    ^
  • End of string
    $
  • A word boundary
    \b
  • Non-word boundary
    \B

Regular Expression
No Match

r"
"
gm

Test String

Code Generator

Generated Code

import java.util.regex.Matcher; import java.util.regex.Pattern; public class Example { public static void main(String[] args) { final String regex = "(?P<preceeding>^(?P<whitespace>(?:[ ]{4}|\\t)+)(?!self\\.)(?P<attrprefix>[a-z0-9_\\.]{1,})?(?P<clsattrname>[A-Z_]{1,}): )(?P<annotation>(?!ClassVar)(?:[A-Za-z0-9_]+\\.*)+(?:(?:(?:\\[?[A-Za-z0-9_]+(?:, | \\| )?)+(?:\\.{3})?)*(?:\\]*))*)+(?P<remainder>.*?$[\\r\\n])"; final String string = "# Regex:\n" + "regex_str = r\"(?P<preceeding>^(?P<whitespace>(?:[ ]{4}|\\t)+)(?!self\\.)(?P<attrprefix>[a-z0-9_\\.]{1,})?(?P<clsattrname>[A-Z_]{1,}): )(?P<annotation>(?!ClassVar)(?:[A-Za-z0-9_]+\\.*)+(?:(?:(?:\\[?[A-Za-z0-9_]+(?:, | \\| )?)+(?:\\.{3})?)*(?:\\]*))*)+(?P<remainder>.*?$[\\r\\n])\"\n\n" + "#pycharm_compatible_version = (?<preceeding>^(?<whitespace>(?:[ ]{4}|\\t)+)(?!self\\.)(?<attrprefix>[a-z0-9_\\.]{1,})?(?<clsattrname>[A-Z_]{1,}): )(?<annotation>(?!ClassVar)(?:[A-Za-z0-9_]+\\.*)+(?:(?:(?:\\[?[A-Za-z0-9_]+(?:, | \\| )?)+(?:\\.{3})?)*(?:\\]*))*)+(?<remainder>.*?$[\\r\\n])\n\n" + "# WARNINGS\n" + "# - Top-level functions and local constants are capture as well if they are written in SCREAMING_SNAKE style!\n" + "#Assumes:\n" + "# - Class variables are named according to SCREAMING_SNAKE convention.\n" + "# - Functions and attributes are named according to underscored_lowercase convention.\n" + "# - Indent -> 4 spaces or 1 tab per level.\n" + "# Notes:\n" + "# - Unannotated variables are skipped\n" + "# - In PyCharm IDE regex replace; replace occurences of ?P< with ?<\n\n" + "import pathlib, os\n" + "TOPLEVEL_CONSTANT: str = 'nomatch' # No match\n\n" + "class TestAttr:\n" + " class TestAttrNested:\n" + " underscore_test = 'asdf'\n\n" + "class SomeClass(ParentClass, SomeMixin):\n" + " FOO_CLS_ATTR: Union[str, int] = 'foo' # Regex should match\n" + " BAR_CLS_ATTR: Sequence[tuple[int, ...]] = ((1, 2), (3, 4)) # Regex should match\n" + " ANNOTATION_AS_ATTR_ATTR: TestAttr.TestAttrNested.underscore_test = 'asdf' # Regex should match\n" + " FIZZ_CLS_ATTR: ClassVar[bool] = True # No match\n" + " BUZZ_CLS_ATTR = 10 # No match (not annotated)\n" + " \n" + " def __init__(self):\n" + " local_instance_attribute: float = 1337.420 # No match\n" + " self.instance_attribute: str = 'NO_MATCH_PLEASE'\n\n" + " class NestedClass:\n" + " NESTED_ATTR: str = 'nested_attribute'\n" + " \n" + " @classmethod\n" + " def nested_method(cls):\n" + " cls.NESTED_ATTR: str = 'should_match' # Regex should match\n" + " print(\"Nested lvl 1!\")\n" + " def arbitrarilyy_nested_func(obj):\n" + " obj.a.b.c.d.ARBITRARILY_NESTED_ATTR: str = 'nested' # Regex should match\n\n" + " @classmethod\n" + " def some_method(cls):\n" + " cls.FOO_CLS_ATTR: str = 'foo' # Regex should match\n" + " cls.instance_attribute.OTHER_CLASATTR: str = 'foo' # Regex should match\n" + " print(cls.FOO_CLS_ATTR) # No Match\n\n" + "def toplevel_func(arg1: int, CONST_ARG: int = 10) -> int: # No match\n" + " MULTIPLIER: float = 6.9\n" + " # ^^ Warning! Constants in top-level functions are captured as well! \n" + " # ^^ Python doesn't support subpatterns AFAIK.\n" + " return arg1*MULTIPLIER\n\n" + "### --> after replacing by ${preceeding}ClassVar[${annotation}]${remainder} ###\n\n" + "class SomeClass(ParentClass, SomeMixin):\n" + " FOO_CLS_ATTR: ClassVar[str] = 'foo' # Regex matches\n" + " BAR_CLS_ATTR: ClassVar[Sequence[int]] = (1, 2, 3)\n" + " FIZZ_CLS_ATTR: ClassVar[bool] = True\n" + " BUZZ_CLS_ATTR = 10 # No match (not annotated)\n" + " instance_attribute: float = 1337.420\n\n" + " class NestedClass:\n" + " NESTED_ATTR: ClassVar[str] = 'nested_attribute'\n" + " \n" + " @classmethod\n" + " def nested_method(cls):\n" + " cls.NESTED_ATTR: ClassVar[str] = 'should_match'\n" + " print(\"Nested lvl 1!\")\n" + " def arbitrarilyy_nested_func(obj):\n" + " obj.a.b.c.d.ARBITRARILY_NESTED_ATTR: ClassVar[str] = 'nested'\n\n" + " @classmethod\n" + " def some_method(cls):\n" + " cls.FOO_CLS_ATTR: ClassVar[str] = 'foo' # Regex matches\n" + " cls.instance_attribute.OTHER_CLASATTR: ClassVar[str] = 'foo'\n" + " print(cls.FOO_CLS_ATTR) # No Match\n\n" + "def toplevel_func(arg1: int, CONST_ARG: int = 10) -> int\n" + " MULTIPLIER: ClassVar[float] = 6.9 \n" + " # ^^ ERRONEOUSLY ADJUSTED...\n" + " # ^^ Warning! Constants in top-level functions are captured as well! \n" + " # ^^ Python doesn't support subpatterns AFAIK.\n" + " return arg1*MULTIPLIER"; final Pattern pattern = Pattern.compile(regex, Pattern.MULTILINE); final Matcher matcher = pattern.matcher(string); while (matcher.find()) { System.out.println("Full match: " + matcher.group(0)); for (int i = 1; i <= matcher.groupCount(); i++) { System.out.println("Group " + i + ": " + matcher.group(i)); } } } }

Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Java, please visit: https://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html