Python for regular expression problem

It's not equal, and there doesn't seem to be such a thing as twice as much as AS.

as) means that the match appears twice

If you need to process a string is"234as"It won't match.

That is, 2 consecutive ASAS will return one.

findall returns allCapture groupof matches. A capture group is a pair of parentheses in regular expression syntax. If there is no capture group in the regular expression, findall returns a match for the entire expression.

You have a capture group (AS) in your regular expression, so findAll() returns a match for this capture group, which is AS.

pythonRegular expressionsAs follows:

In Python, a "regular expression" is a piece of text that is usually used to retrieve and replace a piece of text that conforms to a certain pattern. Specifically, it does the detection of a certain string.

Whether the rules are complied with and the data you want in the web page string is extracted.

A regular expression is a set of rules for string extraction, and we express this rule in a specific syntax in the regular to match the string that satisfies this rule. Regular expressions are general-purpose and can be used not only in Python, but also in other languages.

Programming Features of Python:

Fast speed: The underlying layer of Python is written in C, and many standard and third-party libraries are also written in C, which runs very fast.

Free and open source: Python is a free and open source software (free and open source software).

One. Users are free to distribute copies of the software and read its sources**.

Slow down the changes and use some of it in new free software. Floss is based on the concept of a group sharing knowledge.

High-level language scrambling: Write a program in Python without having to think about low-level details such as how to manage the memory used by your program.

Explanatory: A program written in a compiled language such as C or C++ can be obtained from a source file.

i.e. C or C++) to a language (binary**, i.e. 0s and 1s) that your computer uses. This process goes through the compiler.

and different markers, options to complete.

Python regular expressions are a special character order for which and columnsis a powerful ** used to match strings. The idea is to define a rule for a string in a descriptive language, and if it does, we consider it to be a "match", otherwise the string is invalid.

The way to tell if a string is a legitimate email is:

1. Create a regular expression that matches the email;

2. Use the regular expression to match the user's input to determine whether Li Zhengjiao is legitimate.

Because regular expressions are also represented by strings, it's important to first understand how to describe characters in characters.

In regular expressions, if the character is given directly, it is an exact match. D can match a number, and w can match a letter or number.

Regular expressions (regex) are used to explore fixed patterns in a given string. The pattern we want to find can be anything. You can create patterns similar to finding email messages or mobile phone numbers.

You can also create a pattern that looks for strings that start with a and end with z.

Create a pattern: When using regular expressions, the first thing you need to learn is how to create a pattern. Let's take a look at some of the most commonly used patterns. The simplest pattern that can be thought of is a simple string.

pattern = r'times'

string = it was the best of times, it was the worst of times."

print(len(,string)))

Regular expressions, also known as regular expressions (English: regular expression, often written as regex, regexp or re) in **, is a concept in computer science. Regular expressions are often used to retrieve and replace text that conform to a certain pattern (rule)", so what is the purpose of using regular expressions?

Only two sentences are written in the encyclopedia:

1.Whether a given string conforms to the filtering logic of the regular expression (called a "match").

2.We can use regular expressions to get the specific part we want from the string of character Zen bumpers.

You can simply understand two points: search and, understand the concept and function of regular expressions, let's quickly enter the learning of python! Regular expressions are not unique to Python, but they are undoubtedly the simplest yet most powerful.

A regular expression is a logical formula for string operations, that is, some specific characters and a combination of these specific characters are used to form a "rule string", which is used to express a filtering logic for strings.

Regular expressions are a very powerful tool for matching strings, and the concept of regular expressions is also found in other programming languages, and python is no exception.

Python was designed in the early 1990s by Guido van Rossum of the Dutch Society for Mathematical and Computer Science Research as an alternative to a language called ABC. Python provides efficient high-level data structures and simple and effective object-oriented programming.

Python syntax and dynamic typing, as well as the nature of the interpreted language, have made it a programming language for scripting and rapid application development on most platforms, and with the addition of new language features, it is gradually being used for the development of independent, large-scale projects.

Python regular expressions are strings that use a single string to describe and match a syntactic rule, and are often used to retrieve and replace text that conforms to a certain pattern (rule). The first regular expressions appeared in the theory of automatic control and formal language in theoretical computer science.

In 1950, mathematician Stephen Cole Kleney described the model using mathematical notation called "regular sets." Ken Thompson introduced this symbology to QED, followed by ED on UNIX, and eventually GREP. Since then, regular expressions have been widely used in a variety of UNIX or UNIX-like tools.

Currently, many programming languages support string manipulation using regular table files.

Special characters commonly used for regular expressions:

Mark the next character as a special character, an original character (identity escape, yes"12 in total), a backreferences, or an octal escape. For example, "n" matches the character "n", "n" matches a line break, and "matches" matches "(".

Matches the start position of the input string. If you set a multi-line attribute for a regular expression, you can also match the position after "" or "".

a-z]: a range of characters, matching any character within the specified range. For example, "[a-z]" can match any small line in the range from "a" to "z".

s: Matches any whitespace character, including spaces, tabs, page breaks, etc., equivalent to "[ f t v]". NoteUnicode regular expressions match em-width spaces.