regular-expressions.md

Regular Expressions

Non-special chars match themselves. Exceptions are special characters:

\       Escape special char or start a sequence.

.       Match any char except newline, see re.DOTALL

^       Match start of the string, see 
re.MULTILINE

$       Match end of the string, see re.MULTILINE

[]      Enclose a set of matchable chars

R|S     Match either regex R or regex S.

()      Create capture group, & indicate precedence
After '[', enclose a set, the only special chars are:

]   End the set, if not the first char

-   A range, eg. a-c matches a, b or c

^   Negate the set only if it is the 1st char

Regular Expression Examples

re.findall()

# split all string from a sentence
>>> import re
>>> source = "Python is great!"
>>> re.findall('[\w]+', source)
['Python', 'is', 'great!']

Match hex color value

>>> re.match('^#?([a-f0-9]{6}|[a-f0-9]{3})$', '#ffffff')
<_sre.SRE_Match object at 0x0000000002F04120>
>>> re.match('^#?([a-f0-9]{6}|[a-f0-9]{3})$', '#cdcdcd')
<_sre.SRE_Match object at 0x0000000002EA3160>

Match username doesn't have any special characters

>>> re.match('^[a-zA-Z0-9-_]{3,16}$', 'Check') is not None
True
>>> re.match('^\w|[-_]{3,16}$', 'che%ck') is not None
False

Match email address format

re.match('^([a-z0-9_\.-]+)@([\da-z\.-]+)\.([a-z\.]{2,6})$',
...          'check@example.com')
<_sre.SRE_Match object at 0x0000000002EA3180>

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