Regular Expressions

import re
import this
pattern=r"sonu"

print(re.match(pattern,"Hi this is sonu bisht from dehradun. \nsonu"))
print(re.search(pattern,"Hi this is surendra bisht from dehradun. \nsonu"))
print(re.findall(pattern,"Hi this is sonu bisht from dehradun. \nsonuBisht"))

#### sub function replaces the searched text.

str = "My name is David. Hi David."
pattern = r"David"
newstr = re.sub(pattern, "Surendra", str)
print(newstr)

metacharacters : . (any character); ^ (start of string); $ (end of string)

characterClasses :

[abc][def] will match ad,ae,af,bd,be,bf,cd,ce,cf.

[a-z] ; [A-Z] ;[l-z] ; [0-9] ; [A-Za-z]

pattern = r"[A-Z][A-Z][0-9]"

if re.search(pattern, "LS8"):
print("Match 1")

metacharacter ? means "zero or one repetitions"

pattern = r"colo(u)?r" will match color or colour

9 {1,3} will represent repitition of 9 no of times should be in range of 1 to 3

pattern = r"9{1,3}$"

() brackets denotes group/ we can apply metacharacter * + ? on these

pattern = r"a(bc)(de)(f(g)h)i"

in this bc ,de,fgh and g is a group.

groups() will print all groups catured. groups(0) will show whole string matching. groups(1) shows first group.

gr(a|e)y this represents pattern gray or grey. can also be written as gr[ae]y

specail sequences - \d represents digit, \s represents space, and \w represents word, can be aplhanumeric.

upper case of these is opposite of what they are. i.e. for ex. \D will represent anything other than digit.