RegEx

Settings

Setting	Description
re.match(pattern, string)	First match in string from start
re.search(pattern, string)	First match in string
re.findall(pattern, string)	Find all matches in string
re.sub(pattern, repl, string)	Replace all matches in string
re.compile(pattern, flags=0)	Compile str to RegEx object

Meta Characters

Meta Character	Description	Example
[ ]	Match any character in the brackets	[a-c]
[^ ]	Match any character except in [ ]	[^5]
\	Escape character to escape class or specific match	\d
\d	Escape character for digits	\d
\w	Escape character for word characters	\w
\s	Escape character for whitespace	\s
\S	Escape character for non-whitespace	\S
*	Character occurs 0 or more times	a*
+	Character occurs 1 or more times	a+
?	Character occurs 0 or 1 times	a?
{n}	Character occurs exactly n times	a{3}
{n,}	Character occurs n or more times	a{3,}
|	Either or	a|b

Flags

Flag	long name	Description
re.A	re.ASCII	ASCII only matching
re.I	re.IGNORECASE	Case insensitive matching
re.M	re.MULTILINE	Multiline matching
re.S	re.DOTALL	. special character, matches all characters
re.X	re.VERBOSE	Verbose RegEx
re.L	re.LOCALE	Matching based on locale language

Common Patterns

Remove redundant whitespaces

text = "if     you    want    to    remove    redundant    whitespaces"
re.sub(r"\s+", " ", text)

# >>> 'if you want to remove redundant whitespaces'

Remove special characters

text = "remove # special @@ characters % ..."
re.sub(r"[^a-zA-Z0-9]+", "", text)

## >>> 'remove special characters'

Keep only numeric/alphabetic characters

text = "numbers 123 and letters abc"
re.sub(r"[^a-zA-Z]+", "", text)
re.sub(r"[^0-9]+", "", text)

# >>> 'numbersandletters'
# >>> '123'

Get URLs from text

text = "This is a text with a URL www.google.com and another URL https://www.zhaw.ch"
re.findall(r"https?://\S+|www\.\S+", text)

# >>> ['www.google.com', 'https://www.zhaw.ch']

Get email addresses from text

text = "This is a text with an email hallo@gmail.com"
re.findall("[\w\.-]+@[\w\.-]+\.\w+", text)

# >>> ['hallo@gmailcom']

Get HTML tags from text

text = "This is a text with a <b>bold</b> tag and a <a href='https://www.zhaw.ch'>link</a>"
re.findall(r"<.*?>", text)

# >>> ['<b>', '</b>', '<a href='https://www.zhaw.ch'>', '</a>']

Remove HTML tags from text

text = "This is a text with a <b>bold</b> tag and a <a href='https://www.zhaw.ch'>link</a>"
re.sub(r"<.*?>", "", text)

# >>> 'This is a text with a bold tag and a link'

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