Hướng dẫn dùng regex startswith python
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Hàm endswith[] trong Python xác định xem nếu chuỗi string hoặc chuỗi con đã cho của string [nếu bạn cung cấp chỉ mục bắt đầu beg và chỉ mục kết thúc end] kết thúc với hậu tố suffix thì trả về true, nếu không thì phương thức này trả về false. str.endswith[suffix[, start[, end]]] Các tham số: suffix: Đây có thể là một chuỗi hoặc cũng có thể là một tuple của các tiền tố. start: Chỉ mục bắt đầu. end: Chỉ mục kết thúc. str1 = "Vi du ham endswith trong python...test"; suffix = "test"; print [str1.endswith[suffix]] print
[str1.endswith[suffix, 20]] suffix = "ham" print [str1.endswith[suffix, 2, 4]] print [str1.endswith[suffix, 2, 6]] Kết quả là: I’m sitting in front of my computer refactoring Python code and have just thought of the following question: Can You Use a Regular Expression with the Python The short answer is no. The In
fact, shortly after asking the question, I realized that using a regex with the For example, to check whether a string starts with Python startswith() - A Simple Guide If you already learned something from this tutorial, why not joining my free Python training program? I call it the Finxter Email Computer Science Academy—and it’s just that: a free, easy-to-use email academy that teaches you Python in small daily doses for beginners and pros alike!
How Does the Python startswith() Method Work?Here’s an overview of the str.startswith(prefix[, start[, end]])
Let’s look at some examples using the Python Related article: Python Regex Superpower – The Ultimate Guide Do you want to master the regex superpower? Check out my new book The Smartest Way to Learn Regular Expressions in Python with the innovative 3-step approach for active learning: (1) study a book chapter, (2) solve a code puzzle, and (3) watch an educational chapter video. Python startswith() — Most Basic ExampleSuppose you have a list of strings where each string is a tweet. tweets = ["to thine own self be true",
"coffee break python",
"i like coffee"]Let’s say you work in the coffee industry and you want to get all tweets that start with the string >>> for tweet in tweets:
... if tweet.startswith("coffee"):
... print(tweet)
coffee break python
There is only one tweet in our dataset that starts with the string Python startswith() — Optional ArgumentsThe The start argument tells Thus, the following code outputs the same result as above: >>> for tweet in tweets:
... if tweet.startswith("coffee", 0):
... print(tweet)
coffee break pythonWhat happens if we set >>> for tweet in tweets:
... if tweet.startswith("coffee", 7):
... print(tweet)
i like coffeeWhy does
it print >>> 'i like coffee'.find('coffee')
7Hence, when checking Let’s add another argument – the end index – to the last snippet: >>> for tweet in tweets:
... if tweet.startswith("coffee", 7, 9):
... print(tweet)Nothing is printed on the console. This is because we are only searching over 2 characters – beginning from index 7 (inclusive) and ending at index 9 (exclusive). But we are searching for Now that you know everything about Python’s startswith method, let’s go back to our original question: Can You Use a Regular Expression with the Python startswith() Method?No. The startswith method does not allow for a regular expressions. You can only search for a string. A regular expression can describe an infinite set of matching strings. For example, Instead, you can use the re.match()The The match object contains useful information such as the matching groups and the matching positions. An optional argument Specification: re.match(pattern, string, flags=0) The
Return Value: The [Full Tutorial] Python Regex Match Here’s the video in case you’re more a multimodal learner: Python Regex Match: A Complete Guide to re.match() But is it also true that Python startswith() Tuple – Check For Multiple Strings>>> for tweet in tweets:
... if tweet.startswith(("coffee", "i")):
... print(tweet)
coffee break python
i like coffeeThis snippet prints all strings that start with either What Happens If I Pass A Regular Expression To startswith()?Let’s check whether a tweet starts with any version of the >>> tweets = ["to thine own self be true",
"coffee break python",
"coffees are awesome",
"coffe is cool"]
>>> for tweet in tweets:
if tweet.startswith("coff*"):
print(tweet)
# No output :(This doesn’t work. In regular expressions, Since none of the tweets start with the literal string So you might ask: What Are The Alternatives to Using Regular Expressions in startswith()?There is one alternative that is simple and clean: use the >>> import re
>>> tweets = ["to thine own self be true",
"coffee break python",
"coffees are awesome",
"coffe is cool"]
# Success!
>>> for tweet in tweets:
if re.match("coff*", tweet):
print(tweet)
coffee break python
coffees are awesome
coffe is coolSuccess! We’ve now printed all the tweets we expected. That is, all tweets that start with 💡 Note: This approach is quite slow. Evaluating regular expressions is an expensive operation. But the clarity of the code has improved and we got the result we wanted. Slow and successful is better than fast and unsuccessful. The function
If a matching substring is found, it returns So let’s summarize the article. Summary: Can You Use a Regular Expression with the Python startswith Method?No, you cannot use a regular expression with the Python Given that we can pass a tuple to >>> s = 'a string!'
>>> if s.startswith(['a', 'b', 'c']):
print('yay!')
Traceback (most recent call last):
File "Python raises a >>> if s.startswith(tuple(['a', 'b', 'c'])):
print('yay!')
yay!This works well and is fine performance-wise. Yet, one of Python’s key features is its flexibility. So is it possible to get the same outcome without changing our list of letters to a tuple? Of course! 🙂 We have two options:
The if s.startswith('a') or s.startswith('b') or s.startswith('c'):
# some codeWe write # any takes 1 argument - an iterable
if any([s.startswith('a'),
s.startswith('b'),
s.startswith('c')]):
# some codeThis is much easier to read and is especially useful if you are using many mathematical statements. We can improve this by first creating a
list of conditions and passing this to letters = ['a', 'b', 'c']
conditions = [s.startswith(l) for l in letters]
if any(conditions):
# do somethingAlternatively, we can use letters = ['a', 'b', 'c']
if any(map(s.startswith, letters)):
# do somethingBoth have the same outcome. I personally prefer list comprehensions and think they are more readable. But choose whichever you prefer. Regex HumorPython Regex CourseGoogle engineers are regular expression masters. The Google search engine is a massive text-processing engine that extracts value from trillions of webpages. Facebook engineers are regular expression masters. Social networks like Facebook, WhatsApp, and Instagram connect humans via text messages. Amazon engineers are regular expression masters. Ecommerce giants ship products based on textual product descriptions. Regular expressions rule the game when text processing meets computer science. If you want to become a regular expression master too, check out the most comprehensive Python regex course on the planet:  While working as a researcher in distributed systems, Dr. Christian Mayer found his love for teaching computer science students. To help students reach higher levels of Python success, he founded the programming education website Finxter.com. He’s author of the popular programming book Python One-Liners (NoStarch 2020), coauthor of the Coffee Break Python series of self-published books, computer science enthusiast, freelancer, and owner of one of the top 10 largest Python blogs worldwide. His passions are writing, reading, and coding. But his greatest passion is to serve aspiring coders through Finxter and help them to boost their skills. You can join his free email academy here. |
