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regex in python
Regex, or regular expressions, is a 💪 powerful tool in Python for manipulating 📝 text. It uses special characters and wildcards to define search patterns and extract information from strings. With its range of flags, 📑 functions, and syntax, regex can solve complex text tasks. Python offers many libraries and tools for regex, making it popular for data science and 🌐 web development.
Introduction to Regex in Python
Regular expressions (regex) are powerful tools for matching text patterns in Python. Regex can be used to search for specific text strings, replace certain text strings, validate input, and more. Regex is a powerful language that is used to match patterns in strings and text. Provides a concise and flexible means of identifying text strings of interest, such as A specific letter, word, or pattern of letters. Regex is an essential part of any programming language and Python has a strong regex library that is easy to use.
Regular Expression Syntax
import re pattern = re.compile('\\d+') result = pattern.findall('The price is $20 and the quantity is 3') print(result) # Output: ['20', '3']
The re.compile() function compiles a regular expression pattern into a regular expression object. The regular expression is d+ which matches one or more digits (0-9). The findall() function is, at that point, utilized to search the string for the pattern and return a list of matches. In this illustration, the yield may be a list of strings containing the matched digits '20' and '3'.
Regex Matching in Python
In Python, regex coordinating is done utilizing the re-module. This module gives a number of functions and classes that permit us to explore for designs in a string and manipulate or supplant those patterns when found.
To get begun, we have to import the re-module into our program.
Once the module is imported, you can search for patterns in strings using the re.search() function. This function takes two arguments:
For example, if we wanted to find all instances of the word "cat" in a string, we could use the following code:
my_string = "The cat is in the kitchen" result = re.search("cat", my_string)
If the pattern is found, the result will be a Match object containing information about the match. Otherwise, the result will be None.
We can also use the re.findall() function to find all pattern occurrences in a string. This function takes two arguments:
For example, if we wanted to find all occurrences of the word "cat" in a string, we could use the following code:
my_string = "The cat is in the kitchen" results = re.findall("cat", my_string)
The findall() function results will be a list of all matches of the pattern in the string.
Finally, we can use the re. sub() function to replace all occurrences of a pattern in a string. This function takes three arguments:
For example, if we wanted to replace all occurrences of the word "cat" in a string with the word "dog", we could use the following code:
my_string = "The cat is in the kitchen" result = re.sub("cat", "dog", my_string)
The result of the sub() function will be a new string with all the occurrences of the pattern replaced by the new string.
Regex Searching in Python
Regex searching in Python can be done using the re module. This module provides regular expression matching operations similar to those found in Perl. The module can search for patterns in strings, search and replace operations, and split strings into substrings. To use the re-module, the user must first import it into their program.
import re # Search for occurances of the pattern 'abc' in the string string = 'abcdefghijklmnopqrstuvwxyz' pattern = 'abc' # Use the 'findall' method to return a list of all matches matches = re.findall(pattern, string) # Print the matches print(matches) # Output: ['abc']
This code imports the re-module, which provides regular expression comparison operations similar to Perl. It then defines a string and a pattern to search for. The 'findall' method is used to search for all occurrences of the pattern 'abc' in the string and return a list of all matches. Finally, the matches are printed on the console.
Regex Substitution in Python
Regex replacement in Python is done with the re.sub() function. This function takes three parameters: a regular expression pattern, a replacement string, and the string to do the replacement. It then returns a new string with all pattern matches replaced with the replacement string. Example
import re text = "This is a test string." result = re.sub(r"test", "demo", text) print(result) # Output: This is a demo string.
Grouping and Backreferences in Regex
Grouping and backreferences allow for more complex and powerful regex expressions. The gathering is utilized to group parts of a regex expression to be referenced by a single element, such as a backreference. Backreferences are used to allude to an already matched group inside the same expression. For illustration, in case a regex expression contains two bunches (e.g., w+ and d+), a backreference can allude to the first group when utilized within the second group, permitting the regex expression to match different strings with the same pattern. This can be valuable for matching patterns that can appear at different times in a string, such as a phone or credit card number.
Examples of Regex in Python
#1 Match all alphanumeric characters import re pattern = r"[a-zA-Z0-9]" #2 Match all alphanumeric characters and underscore import re pattern = r"[a-zA-Z0-9_]"
This code employments normal expressions to coordinate all alphanumeric characters and underscores. The r"[a-zA-Z0-9_]" tells the regex engine to match any character within the range of a-z, A-Z, 0-9, and the underscore character. The regular expression is put away within the variable pattern.
Regular expressions (regex) in Python may be an effective instrument for pattern matching, text manipulation, and input validation. With regex, designers can effortlessly perform complex text tasks by defining search patterns with uncommon characters and wildcards, making it a basic part of data science and web improvement. Python contains a solid regex library that's simple to utilize and offers a range of functions and classes for regex matching, searching, and substitution.
Answer:c. To find the first match in a string
import re string = "Python is a great language" pattern = r"great" print(re.findall(pattern, string))
b. ["Python", "great", "language"]
c. ["Python", "is", "a", "great", "language"]
Answer:b. re.match() looks for a pattern anywhere within the string, whereas re.search() looks for a pattern at the starting of a string.