Python - Check if a string matches regex list

A regular expression is also referred as regex, which is a sequence of characters that forms a search pattern. It's one of the powerful tools used for pattern matching and manipulating strings. In python we are having a module called re which helps to form a regular expression.

Regex patterns consist of ordinary characters such as letters, digits and special characters called metacharacters. Meta Characters have special meanings and allow us to define complex search patterns. The below are some commonly used meta characters in python regular expressions.

• . (dot) − Matches any single character except a newline.

• ^ (caret) − Matches the start of a string.

• $ (dollar) − Matches the end of a string.

• * (asterisk) − Matches zero or more occurrences of the preceding pattern.

• + (plus) − Matches one or more occurrences of the preceding pattern.

• ? (question mark) − Matches zero or one occurrence of the preceding pattern.

• [] (square brackets) − Defines a character class and matches any single character within the brackets.

• () (parentheses) − Groups patterns together and captures matched substrings.

• \ (backslash) − Escapes a metacharacter or introduces a special sequence.

The other Additional regular expressions support special sequences that represent common patterns are mentioned as below.

• \d − Matches any digit equivalent to [0-9].

• \w − Matches any alphanumeric character equivalent to [a-zA-Z0-9_].

• \s − Matches any whitespace character.

• \b − Matches a word boundary.

• \A − Matches the start of a string similar to ^, but it doesn't respect multiline mode.

• \Z − Matches the end of a string similar to $, but it doesn't respect multiline mode.

There are multiple approaches in python to check if a string matches a regular expression (regex) list. Let’s see each approach one by one.

Using re module

The 're' module in Python provides functions to work with regular expressions. We can use the 're.match()' function in re module to check if a string matches a regex pattern and to check a list of regex patterns, we can iterate over the list and call 're.match()' for each pattern.

Example

In this example, the re.match() function is used to check if the string matches each pattern in the regex_list. If match is found, it will print the pattern.

import re
string = "Hello, Welcome to Tutorialspoint!"
regex_list = [r"Hello", r"\bWelcome\b", r"\d+"]
for pattern in regex_list:
   if re.match(pattern, string):
      print(f"String matches pattern: {pattern}")

Output

String matches pattern: Hello

Using list comprehension and re.search()

The other way of finding the matched pattern is to use list comprehension and the re.search() function. By using the list comprehension without iterating over the regex list, we can create a new list containing the matching patterns.

Example

In this example, we are using the list comprehension with the line of code [pattern for pattern in regex_list if re.search(pattern, string)] which creates a new list matching_patterns that contains the regex patterns from regex_list that match the string. Then we use the re.search() function to find the first occurrence of a pattern in the string.

import re
string = "Hello,happy learning!"
regex_list = [r"Hello", r"\bWelcome\b", r"\d+"]
matching_patterns = [pattern for pattern in regex_list if re.search(pattern, string)]
print("Matching patterns:", matching_patterns)

Output

Matching patterns: ['Hello']

Using the any() function and re.search()

The any() function is one of the functions available in python which can be used to check if any element in a sequence of the regex list is true. We can combine this with re.search() to check if any regex pattern matches the string.

Example

In this example, the any() function is used to iterate the elements of the regex list and check if any pattern matches the string using re.search(). If match is found, it will print "String matches at least one pattern".

import re
string = "Hello, Welcome to Tutorialspoint!"
regex_list = [r"Hello", r"\bWelcome\b", r"\d+"]
if any(re.search(pattern, string) for pattern in regex_list):
   print("String matches at least one pattern")

Output

String matches at least one pattern