How can I match the start and end in Python\'s regex?

In Python, the re module is used to work with regular expressions. In some cases, we need to check whether a string starts or ends with a specific pattern, and then we need to use special regex characters called anchors. Following are the anchors used in regular expressions −

• ^ − This anchor matches the beginning of a string.
• $ − This anchor matches the end of a string.

Python Regex Methods

The following methods from the re module are commonly used to apply start and end matching −

• re.match(): Checks for a match only at the beginning of the string.
• re.search(): Scans the entire string for a match.
• re.fullmatch(): Matches the entire string against the pattern.

Match a String that Starts with a Word

To match a string that starts with a specific word, we need to place the "^" symbol before the word and pass it as a pattern to the re.match() method.

Since "^" matches the beginning of the string, this pattern matches a string only if it starts with the specified word ?

import re

text = "Welcome to Tutorialspoint"
if re.match(r"^Welcome", text):
    print("Starts with 'Welcome'")
else:
    print("Does not start with 'Welcome'")

Starts with 'Welcome'

Match a String that Ends with a Word

Similarly, to match a string that ends with a specific word, we need to place the "$" symbol after the word and pass it as a pattern to the re.search() method.

Since "$" matches the end of the string, this pattern matches a string only if it ends with the specified word ?

import re

text = "Learn Python Programming"
if re.search(r"Programming$", text):
    print("Ends with 'Programming'")
else:
    print("Does not end with 'Programming'")

Ends with 'Programming'

Match an Entire String Using "^" and "$"

If we want to match an entire string exactly, from the beginning to the end, we can combine the anchors "^" and "$". If the pattern is the desired word/regex placed between these two symbols, the re.match() matches a string that starts and ends with the specified pattern ?

import re

text = "admin123"
pattern = r"^admin\d{3}$"

if re.match(pattern, text):
    print("Exact pattern matched")
else:
    print("No match")

Exact pattern matched

Match Lines Individually Using re.MULTILINE

When we are working with multi-line strings and we want to match each single line individually, then we can use ^ and $ anchors to match each line by using the re.MULTILINE flag ?

import re

text = "Start now\nStart again\nFinish later"
matches = re.findall(r"^Start", text, re.MULTILINE)
print(matches)

['Start', 'Start']

Using re.fullmatch() for Exact String Match

The re.fullmatch() method in Python accepts a pattern and string as parameters and matches the given pattern in the specified string. In case of a match, it returns the match object and returns None if there are no matches.

The re.match() or re.search() methods match only part of the string, whereas, re.fullmatch() method only returns a match if the whole string satisfies the pattern ?

import re

text = "Python3.11"
pattern = r"Python3\.\d{2}"

if re.fullmatch(pattern, text):
    print("Full match found")
else:
    print("No full match")

Full match found

Comparison of Methods

Conclusion

Use ^ and $ anchors to match string start and end positions. The re.fullmatch() method provides the most precise matching for complete string validation.