How does [d+] regular expression work in Python?

Regular expressions are a useful tool for searching and manipulating strings in Python. Among the several patterns and methods available, the [d+] expression is used to match one or more digits in a string.

In this article, we will go over the [d+] regular expression pattern, the way it is used, and five code examples with step-by-step explanations to help you understand and apply it to your Python projects.

Understanding the [d+] Pattern

Before we see the code examples, let us first understand the [d+] pattern. So basically [d+] is a combination of two elements -

• [d]: This is a shorthand character class for the digits 0 to 9.

• [+]: This is a quantifier that indicates "one or more" of the preceding pattern.

• Combining these two elements, [d+] creates a pattern that matches one or more consecutive digits in a string.

Example: Basic usage of [d+]

In this example, we will define a [d+] pattern and search for one or more consecutive digits in the given phone number string. If the re.search() function returns a match object, we print 'True', otherwise, we print 'False'.

import re

phone_number = '234567890'
pattern = r'\d+'

result = re.search(pattern, phone_number)

if result:
    print('True')
else:
    print('False')

After running the program, you will get this result -

True

Example: Matching a Specific Number

The below Python program will check if a password has three numbers in a row or not. It basically uses a regular expression to find the pattern. And if it finds the pattern, it will print True; otherwise, it prints False.

import re

password = 'mypassword123'
pattern = r'\d{3}'

result = re.search(pattern, password)

if result:
    print('True')
else:
    print('False')

This output will be displayed when the program runs -

True

Matching a with one or More "d"

In this Python program, we are going to check whether there are any numbers or digits present in a given string. We will use regular expressions to find one or more digits. The search() method will find the first match in the string. So if a match is found, it will print the number with the help of group() and group(0).

import re

# Define the regular expression pattern
pattern = r'd+'  

# Define the string to be searched
string = 'dddabc abiuwdd oiwddd'

# Use the search() method here
matches = re.findall(pattern, string)

print(matches)

# Define a capture group to capture the match
pattern = r'\d+' 
matches = re.search(pattern, string, re.MULTILINE)
if matches:
    # Print the match
    print(matches.group(0))

Output

After running the program, you will get this result -

ddd
ddd

Using a Lookahead

To match a string with one or more "d" characters and use a lookahead, we can use the following program -

import re

# Define the regular expression pattern
pattern = r'd+(?=abc)';

# Define the string to be searched
string = 'dddabc'

# Use the search() method here
matches = re.search(pattern, string)

# Print the match
if matches:
    print(matches.group())

You will see this result after executing the program -

ddd

Using a Capture Group

To match a string with one or more "d" characters and use a capture group, we can use the following code -

import re

# Define the regular expression pattern
pattern = r'd+(?P<abc>abc)';

# Define the string to be searched
string = 'dddabc'

# Use the search() method here
matches = re.search(pattern, string)

# Print the match
if matches:
    print(matches.group())
    print(matches.group('abc'))

The program gives this output when it is run -

dddabc
abc