ฝึกพูดภาษาอังกฤษด้วยเทคนิค Shadowing จากวิดีโอ: [Practice Problems] Regular Expressions (Regex) - Visually Explained

Have you tried our regular expressions practice exercises?

If you have, great!

We're going to work through the solutions now.

If not, the problems are linked in the description.

Alright, let's start with problem one.

In this problem, we want to match all the phone numbers from the bulletin board text.

Each phone number follows the format.

A fixed area code, and a hyphen, followed by three digits, another hyphen, and a final four digits.

Since every phone number starts with the same area code and hyphen, we write the literal characters 1, 2, 3, hyphen directly into the pattern box.

Next, the middle group of numbers can have any combination of three digits.

To match this, we use the character class 0 through 9 to match a single digit

and follow it with the quantifier 3 to match exactly 3.

Following the character class, we write another literal hyphen.

To match the last four digits, like the middle three, we use a character class with 0 through 9.

But to match four digits instead of 3, we use a quantifier of 4.

Great!

As we can see, this pattern matches both phone numbers and our bulletin board text.

Fixed quantifiers like 3 and 4 are ideal when you know the exact length you're looking for.

Phone numbers, zip codes, product codes, anything with a predictable structure.

Quantifiers will also be quite useful in problem 2.

In this problem, we want to write a regular expression to match all the prices in our text string.

each price starts with a dollar sign followed by one

or more digits a dot

and exactly two digits for cents you might be tempted to start by writing the literal dollar sign character

but in regex dollar sign is a special syntax

that means end of line

so it won't match the dollar sign character to match a

literal dollar sign we put a backslash in front of it after the dollar sign comes the digits before the decimal,

which we can match using a character class with 0 through 9.

Since there could be any number of digits before the decimal, we use the plus quantifier to match one or more digits.

Following this character class, we specify a dot.

Remember, like the dollar sign, the dot is special syntax, called a wildcard, that matches any single character.

To use a literal dot character, we need to write a backslash before it.

Finally, cents always have exactly two digits.

To match this, we write a character class allowing the digits 0 through 9 and a quantifier of 2.

Awesome!

With this pattern, all five prices are matched.

Before we move on, we've now written the character class containing 0 through 9 several times.

Since this is such a common pattern, regex syntax actually provides a shorthand for it.

Instead of explicitly writing the character class, we write backslash d, which also means any digit.

Awesome, our pattern is now more concise and we still get the same matches.

We'll use the digit shorthand backslash d again in problem 3.

In this problem, we want to match all the dates in the text.

Each date has a month name, a day number, and a four-digit year.

We'll start by matching the month names.

Month names are made up of letters, both upper and lowercase, so we'll use a character class of all the uppercase and lowercase letters.

To match one or more letters, we follow the class with the plus quantifier.

After the month name comes a literal space.

After the space, the day can be one digit or two.

To match exactly one or two digits,

we use the backslash d shorthand followed by a range quantifier with a lower bound of one and upper bound of two.

Following the day, we write a literal comma and space.

Lastly, the year is always four digits, so we write the digit shorthand and a quantifier of four.

Awesome!

With that pattern, we've matched all the dates.

With these practice problems, you've seen how to write patterns for three different data types.

If you want to go deeper on any of the concepts we used in this video, check out our regular expressions intro video linked in the description.

We're working on lots more Python explainer videos like this one, so be sure to subscribe so that you don't miss out.

If you have any questions or topics that you'd like to learn about, let us know in the comments below.

We'd love to hear from you.

Thanks for watching!

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ฝึกพูดภาษาอังกฤษด้วยเทคนิค Shadowing จากวิดีโอ: [Practice Problems] Regular Expressions (Regex) - Visually Explained

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