Regular Expression Tutorial – Day 14

Topic – Regular Expression Tutorial

Define Regular Expression in layman’s term

In simple terms, a regular expression, often referred to as a “regex,” is a sequence of characters that forms a search pattern. It is used for matching strings or parts of strings, helping you find specific patterns within a larger piece of text.

To give you an example, consider a situation where you’re searching for phone numbers within a long document. Instead of reading every line to find each number, you can use a regular expression that represents the pattern of a typical phone number. This can help you quickly identify and extract all the phone numbers in the text, saving you time and effort.

In summary, regular expressions serve as powerful tools to help you search, manipulate, and manage text by identifying specific patterns or sequences of characters. They are widely used in various programming languages and text editing applications to facilitate tasks like data validation, searching, and replacing text, and data extraction.

Regular Expression Tutorial

20 Regular Expression Questions

1.What is a regular expression?

Answer: A regular expression, often abbreviated as regex, is a sequence of characters that defines a search pattern.

2. What are the benefits of using regular expressions?

Answer: Regular expressions allow for powerful and flexible pattern matching, making it easier to perform complex search and replace operations in text.

3.How do you create a basic regular expression in Python?

Answer: Use the re module in Python to create a basic regular expression.

Example code:

import re
pattern = r”hello”
text = “hello world”
result = re.search(pattern, text)

4. What is the purpose of the ‘re.search()’ function in Python?

Answer: The re.search() function is used to search for a match to a pattern within a string.

5.How do you match the beginning of a string in a regular expression?

Answer: Use the ^ symbol to match the beginning of a string.

Example code:

pattern = r”^hello”
text = “hello world”
result = re.search(pattern, text)

6.How do you match the end of a string in a regular expression?

Answer: Use the $ symbol to match the end of a string.

Example code:

pattern = r”world$”
text = “hello world”
result = re.search(pattern, text)

7.How do you match any single character in a regular expression?

Answer: Use the . symbol to match any single character.

8.How do you match any single digit in a regular expression?

Answer: Use the \d pattern to match any single digit.

9.How do you match any single word character in a regular expression?

Answer: Use the \w pattern to match any single word character.

10.How do you match any single whitespace character in a regular expression?

Answer: Use the \s pattern to match any single whitespace character.

11.How do you match a specific set of characters in a regular expression?

Answer: Use square brackets [] to create a character set.

Example code:

pattern = r”[aeiou]”
text = “hello world”
result = re.findall(pattern, text)

12.How do you match a specific range of characters in a regular expression?

Answer: Use a hyphen – to specify a range of characters within square brackets.

13.How do you match a specific set of characters or digits in a regular expression?

Answer: Use the | symbol to match any of the specified patterns.

Example code:

pattern = r”cat|dog”
text = “I have a cat and a dog”
result = re.findall(pattern, text)

14.How do you match a specific number of occurrences of a character in a regular expression?

Answer: Use the {} curly brackets to specify the number of occurrences.

15.How do you match zero or more occurrences of a character in a regular expression?

Answer: Use the * symbol to match zero or more occurrences.

16.How do you match one or more occurrences of a character in a regular expression?

Answer: Use the + symbol to match one or more occurrences.

17.How do you match zero or one occurrence of a character in a regular expression?

Answer: Use the ? symbol to match zero or one occurrence.

18.How do you match a specific word in a regular expression?

Answer: Use the word itself to match the word in the text.

Example code:

pattern = r”hello”

text = “hello world”

result = re.search(pattern, text)

19.How do you match the opposite of a specified pattern in a regular expression?

Answer: Use the ^ symbol inside square brackets to match the opposite of a pattern.

20.How do you match the occurrence of a character at the beginning of a word in a regular expression?

Answer: Use the \b pattern to match the beginning of a word.

Complex Regular Expression Questions

Here are 10 complex regular expression questions in Python along with their answers:

Question 1: Check if a string contains only letters (both lowercase and uppercase).

import re
pattern = “^[a-zA-Z]+$”
string = “AbCdEfG”
result = re.match(pattern, string)
print(bool(result))

Question 2: Check if a string contains at least one digit.

import re
pattern = “.\d+.“
string = “abc123”
result = re.match(pattern, string)
print(bool(result))

Question 3: Extract all email addresses from a string.

import re
pattern = r'[\w.-]+@[\w.-]+’
string = “Contact us at support@example.com or info@example.net”
result = re.findall(pattern, string)
print(result)

Question 4: Replace all occurrences of ‘is’ with ‘was’ in a string.

import re
pattern = r’\bis\b’
string = “He is happy, she is sad, it is raining.”
result = re.sub(pattern, ‘was’, string)
print(result)

Question 5: Check if a string starts with a capital letter.

import re
pattern = “^[A-Z].*”
string = “Hello”
result = re.match(pattern, string)
print(bool(result))

Question 6: Split a string into words.

import re
string = “This is a sample string.”
result = re.split(r’\s’, string)
print(result)

Question 7: Validate a phone number (XXX-XXX-XXXX) format.

import re
pattern = r’\d{3}-\d{3}-\d{4}’
string = “123-456-7890”
result = re.match(pattern, string)
print(bool(result))

Question 8: Extract all words that start with ‘a’ or ‘b’.

import re
pattern = r’\b[a-b]\w*’
string = “An apple a day keeps the doctor away, but a banana works too.”
result = re.findall(pattern, string)
print(result)

Question 9: Check if a string has at least 5 characters.

import re
pattern = r’^.{5,}$’
string = “Hello”
result = re.match(pattern, string)
print(bool(result))

Question 10: Remove all punctuation from a string.

import re
string = “Hello, World! This is a sample string.”
result = re.sub(r'[^\w\s]’, ”, string)
print(result)

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