Learn RE – Regular Expressions in Python

Learn RE – Regular Expressions in Python: Regular Expressions (sometimes shortened to regexp, regex, or re) are a tool for matching patterns in text.

In Python, we have the re module. The applications for regular expressions are wide-spread, but they are fairly complex, so when contemplating using a regex for a certain task, think about alternatives, and come to regexes as a last resort.

An example regex is:

r"^(From|To|Cc).*[email protected]"

Now for an explanation: the caret ^ matches text at the beginning of a line. The following group, the part with (From|To|Cc) means that the line has to start with one of the words that are separated by the pipe |. That is called the OR operator, and the regex will match if the line starts with any of the words in the group. The .*? means to un-greedily match any number of characters, except the newline \n character. The un-greedy part means to match as few repetitions as possible. The . character means any non-newline character, the * means to repeat 0 or more times, and the ? character makes it un-greedy.

So, the following lines would be matched by that regex: From: [email protected] To: !asp]<,. [email protected]

A complete reference for the re syntax is available at the python docs (re-regular expressions.)

As an example of a “proper” email-matching regex (like the one in this exercise), see this: Mail::RFC822::Address: regexp-based address validation

# Exercise: make a regular expression that will match an email. this is the answer code
import re
def test_email(your_pattern):
    pattern = re.compile(your_pattern)
    emails = ["[email protected]", "[email protected]", "wha.t.`1an?ug{}[email protected]"]
    for email in emails:
        if not re.match(pattern, email):
            print("You failed to match %s" % (email))
        elif not your_pattern:
            print("Forgot to enter a pattern!")
# Your pattern here!
pattern = r"\"?([-a-zA-Z0-9.`?{}]+@\w+\.\w+)\"?"

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About the Author: Bernard Aybout

In the land of bytes and bits, a father of three sits, With a heart for tech and coding kits, in IT he never quits. At Magna's door, he took his stance, in Canada's wide expanse, At Karmax Heavy Stamping - Cosma's dance, he gave his career a chance. With a passion deep for teaching code, to the young minds he showed, The path where digital seeds are sowed, in critical thinking mode. But alas, not all was bright and fair, at Magna's lair, oh despair, Harassment, intimidation, a chilling air, made the workplace hard to bear. Management's maze and morale's dip, made our hero's spirit flip, In a demoralizing grip, his well-being began to slip. So he bid adieu to Magna's scene, from the division not so serene, Yet in tech, his interest keen, continues to inspire and convene.