String and Line Anchors in Regular Expressions and Python

Today we are going to take a look at the string and line anchors in regular expressions, and also how to use these in python. An anchor will match comparing the beginning and/or ends of a string.

The anchor at the beginning of a string is the symbol ^. The anchor at the end of a string is $.

If we want to match a string that ends in a number, and don’t care what’s before that number, our regular expression would look like this:

.*[0-9]$

In the pattern, .* matches with any character while [0-9]$ ensures the string ends with a number.

Now let’s talk about the opposite. Let’s say we want a match when the string starts with a number. Then the regular expression would look like this.

^[0-9].*

This would match with this string:

5 asdf

Line Anchors with Regular Expressions in Python

Let’s say we have a string in python with multiple lines. And we want a match with each line that ends in a number.

import re

test = '''
this will match 1
this will also match 2
This 3 will not match
'''

# the third parameter makes it multiline
results = re.findall(r'.*[0-9]$', test, re.M)

print(results)

The thing to take note here, for python to know it’s a multiline, we pass in the flag re.M as the third parameter. Without it, it will only match with the first line in the string.

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