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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
Processing...

Test String

Substitution
Processing...

Code Generator

Language

Generated Code

import re regex = re.compile(r"(?<=^|[^_])__(((\\_)|((?![\s_])(?:(?:[^_]|_(?!_))+?)?[^\s_]))+)__(?=[^_]|$)", flags=re.MULTILINE) test_str = ("-- funciona\n" "__foo bar__\n" "__f o o b a r__\n" "**teste __lorem ipsum__ dolor sit**\n" "__teste **lorem ipsum** dolor sit__\n" "abc__xyz__teste\n\n" "-- não funcionava na primeira versão\n" "__foo_bar__\n" "__a__\n" "__*__\n" "__foo_*bar__\n\n" "-- não é para funcionar\n" "__ foo bar__\n" "__foo bar __\n" "_foo__\n" "__ foo __\n" "_foo_\n" "__foo_\n" "__ __\n" "__a____\n" "____a__\n" "_____\n\n" "-- corner case: aninhado (não tratei pois não sei o que deveria fazer)\n" "__abc__xyz__123__\n" "__abc __xyz__ 123__\n\n" "-- corner case: escape (chega a reconhecer alguns casos, mas não substitui \"\\_\" por \"_\"\n" "__\\___\n" "__a\\___\n" "__abc\\___\n" "__\\_abc_\\__ -- errado, mas não consegui tratar") subst = "<i>\\1<\\i>" result = regex.sub(subst, test_str) if result: print(result)

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 Python, please visit: https://docs.python.org/3/library/re.html