Regular Expression (RE)
They can be used with string operations.
Using this, we specify the rules for the set of possible strings that we want to match (Searching for patterns in another string).
Note : its finds FIRST instance of that pattern
We can also use REs to modify a string or to split it apart in various ways.
To use this ,
Import re
We need to import the above module.
Functions in RE module
Search
Syntax:
match = re.search(pat, text
Here, Match > match object
Re. > used to call function in module RE
Ex:
match = re.search(‘iig’,'called piiiig')
Now to see the result , we can use
Match.group()
>>> m.group()
'iig'
It will show us the result of the match.
A function for this can be –
def Find(pat,text):
m =re.search(pat,text)
if m:print (m.group())
else : print('not found')
Now we see some matches for function ‘Find’
>>> Find('ig','i am a piiiig')
ig
>>> Find('...g','i am a piiiig')
iiig
>>> Find('p...g','i am a piiiig')
not found
>>> Find('p....g','i am a piiiig')
piiiig
>>> Find('p....g','i am a piiiigand no ghgg')
piiiig
>>> Find('g..g','i am a piiiigand no ghgg')
ghgg
>>> Find('g..g','i am a piiiigand no gtrg ghgg')
gtrg
>>> Find('g..g','i am a piiiigand no gtrg ghgg')
gtrg
>>> Find('g..g','i am a piiiigand no gbng gtrg ghgg')
Gbng
Note : As we can see, only first instance is displayed here.
The Dot operator (.) is like blanks which can be anything.
Raw string - >>> Find(r'p\.i','i am a p.iiiigand no gbng gtrg ghgg')
p.i
Slash ( \ )
Regular expressions use the backslash character ('\') to indicate special forms or to allow special characters to be used without invoking their special meaning.
>>> Find(r'\\','i am a p.\iiiigand no gbng gtrg ghgg')
\
>>>Find(r'\\ii..','i am a p.\iiiigand no gbng gtrg ghgg')
\iiii
>>> find('\*','hi*+ther tether')
*
>>> find('\+','hi*+ther tether')
+
\w operator
Finds letters after a special symbol
I mean \w will find 1.
\w\w will find 2 .
Ex: >>> find(r':\w\w','song :hi re hi')
:hi
The no. of letters can be any number .
Ex2: >>> find(r':\w\w','song :hi re hi')
:hi
It finds the 1st 3 letters of the sentence.
Ex3: >>> find(r';\w\w\w','song ;hithere hi again')
;hit
As you can see, it can match any part after any symbol.
Ex4: This is another way which will show all the letters till we reach a blank.
>>> match = re.search(':\w+','123edit :the fucking line')
>>> match.group()
':the'
Now if we want to see the rest of the sentence from the search point .-
>>> match = re.search(':\w.+','123edit :the fucking line')
>>> match.group()
':the fucking line'
The dot sign means all after that point.
Now take this example . If we have an email address like - arin.thearc@gmail.com
>>> match = re.search('\w+@\w+','arin.thearc@gmail.com')
>>> match.group()
'thearc@gmail'
Using above method will not display anything after dot(.) sign . So ,
>>> match = re.search('[\w.]+@[\w.]+','arin.thearc@gmail.com')
>>> match.group()
'arin.thearc@gmail.com'
Here , the brackets are used to allow a special symbol to be allowed to be read .
\d operator
Digit finder. Finds digits occurrence anywhere.
>>> find(r'\d\d\d','song :re 123xxx')
123
>>> find(r'\d\d\d','song :re sss123xxx')
123
>>> match = re.search('\d','123edit the fucking line')
>>> match.group()
'1'
>>> match = re.search('\d+','123edit the fucking line')
>>> match.group()
'123'
White space charatcters
Blank space , tabs all come under white space .
A ‘\s’ detects every one.
>>> find(r'\d\s\d\s\d','1 2 3')
1 2 3
Non-White space charatcters
A capital s ‘S’ is for non-white space.
>>> find(r':\S+','blabuuu4564&======booo :oyehoye puttar' )
:oyehoye
+ sign
Causes the resulting RE to match 1 or more repetitions of the preceding RE
>>> find(r'\d\s+\d\s+\d','1 2 3')
1 2 3
>>> find(r':\w+','bla buuu booo :oyehoye' )
:oyehoye
The above code will match any length after the colon .
>>> find(r'\w+','blabuuu booo :oyehoye' )
Blabuuu
The above code will match the 1st word completely.
Note : anything can be a woed , but not space.
See the code below
>>> find(r'\w+','blabuuu4564 booo :oyehoye' )
blabuuu4564
>>> find('.+','blabuuu4564&booo :oyehoye' )
blabuuu4564&booo :oyehoye
So what the + does is , its greedy . It goes as far as it can, and then it stops.
Dot operator( . )
In the default mode, this matches any character except a newline
>>> find('.','blabuuu4564&booo :oyehoye' )
b
>>> find('.+','blabuuu4564&booo :oyehoye' )
blabuuu4564&booo :oyehoye
This is a work in progress. i will add to it gradually .
