Python RegEx: re.match(), re.search(), re.findall() with Example

What is Regular Expression in Python?

A Regular Expression (RE) in a programming language is a special text string used for describing a search pattern. It is extremely useful for extracting information from text such as code, files, log, spreadsheets or even documents.

For example, consider the following code of Python re.match() function. The expression “w+” and “\W” will match the words starting with letter ‘g’ and thereafter, anything which is not started with ‘g’ is not identified. To check match for each element in the list or string, we run the forloop in this Python re.match() Example.

re.search(): Finding Pattern in Text

re.search() function will search the regular expression pattern and return the first occurrence. Unlike Python re.match(), it will check all lines of the input string. The Python re.search() function returns a match object when the pattern is found and “null” if the pattern is not found

How to use search()?

In order to use search() function, you need to import Python re module first and then execute the code. The Python re.search() function takes the “pattern” and “text” to scan from our main string

For example here we look for two literal strings “Software testing” “guru99”, in a text string “Software Testing is fun”. For “software testing” we found the match hence it returns the output of Python re.search() Example as “found a match”, while for word “guru99” we could not found in string hence it returns the output as “No match”.

How to Use re.findall() in Python?

Here we have a list of e-mail addresses, and we want all the e-mail addresses to be fetched out from the list, we use the method re.findall() in Python. It will find all the e-mail addresses from the list.

Here is the complete code for Example of re.findall()

import re

list = ["guru99 get", "guru99 give", "guru Selenium"]
for element in list:
    z = re.match("(g\w+)\W(g\w+)", element)
if z:
    print((z.groups()))
    
patterns = ['software testing', 'guru99']
text = 'software testing is fun?'
for pattern in patterns:
    print('Looking for "%s" in "%s" ->' % (pattern, text), end=' ')
    if re.search(pattern, text):
        print('found a match!')
else:
    print('no match')
abc = 'guru99@google.com, careerguru99@hotmail.com, users@yahoomail.com'
emails = re.findall(r'[\w\.-]+@[\w\.-]+', abc)
for email in emails:
    print(email)

Python Flags

Many Python Regex Methods and Regex functions take an optional argument called Flags. This flags can modify the meaning of the given Python Regex pattern. To understand these we will see one or two example of these Flags.

Various flags used in Python includes

Example of re.M or Multiline Flags

In multiline the pattern character [^] match the first character of the string and the beginning of each line (following immediately after the each newline). While expression small “w” is used to mark the space with characters. When you run the code the first variable “k1” only prints out the character ‘g’ for word guru99, while when you add multiline flag, it fetches out first characters of all the elements in the string.

Here is the code

import re
xx = """guru99 
careerguru99	
selenium"""
k1 = re.findall(r"^\w", xx)
k2 = re.findall(r"^\w", xx, re.MULTILINE)
print(k1)
print(k2)

• We declared the variable xx for string ” guru99…. careerguru99….selenium”
• Run the code without using flags multiline, it gives the output only ‘g’ from the lines
• Run the code with flag “multiline”, when you print ‘k2’ it gives the output as ‘g’, ‘c’ and ‘s’
• So, the difference we can see after and before adding multi-lines in above example.

Likewise, you can also use other Python flags like re.U (Unicode), re.L (Follow locale), re.X (Allow Comment), etc.

Python 2 Example

Above codes are Python 3 examples, If you want to run in Python 2 please consider following code.

# Example of w+ and ^ Expression
import re
xx = "guru99,education is fun"
r1 = re.findall(r"^\w+",xx)
print r1

# Example of \s expression in re.split function
import re
xx = "guru99,education is fun"
r1 = re.findall(r"^\w+", xx)
print (re.split(r'\s','we are splitting the words'))
print (re.split(r's','split the words'))

# Using re.findall for text
import re

list = ["guru99 get", "guru99 give", "guru Selenium"]
for element in list:
    z = re.match("(g\w+)\W(g\w+)", element)
if z:
    print(z.groups())
    
patterns = ['software testing', 'guru99']
text = 'software testing is fun?'
for pattern in patterns:
    print 'Looking for "%s" in "%s" ->' % (pattern, text),
    if re.search(pattern, text):
        print 'found a match!'
else:
    print 'no match'
abc = 'guru99@google.com, careerguru99@hotmail.com, users@yahoomail.com'
emails = re.findall(r'[\w\.-]+@[\w\.-]+', abc)
for email in emails:
    print email

# Example of re.M or Multiline Flags
import re
xx = """guru99 
careerguru99	
selenium"""
k1 = re.findall(r"^\w", xx)
k2 = re.findall(r"^\w", xx, re.MULTILINE)
print k1
print k2

Test your Python Knowledge

Summary

A regular expression in a programming language is a special text string used for describing a search pattern. It includes digits and punctuation and all special characters like $#@!%, etc. Expression can include literal

• Text matching
• Repetition
• Branching
• Pattern-composition etc.

In Python, a regular expression is denoted as RE (REs, regexes or regex pattern) are embedded through Python re module.

• “re” module included with Python primarily used for string searching and manipulation
• Also used frequently for webpage “Scraping” (extract large amount of data from websites)
• Regular Expression Methods include re.match(),re.search()& re.findall()
• Other Python RegEx replace methods are sub() and subn() which are used to replace matching strings in re
• Python Flags Many Python Regex Methods and Regex functions take an optional argument called Flags
• This flags can modify the meaning of the given Regex pattern
• Various Python flags used in Regex Methods are re.M, re.I, re.S, etc.