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Preface

If you search the Internet for Python regular expressions, you will see a lot of junk articles that write code like this:

Import repattern = re.compile ('regular expression') text = 'segment string' result = pattern.findall (text)

The authors of these articles may have been influenced by the bad habits of other languages, or they may have been misled by other junk articles and used them without thinking.

In Python, you really don't need to use re.compile!

To prove this, let's look at the source code of Python.

Enter: in PyCharm:

Import rere.search

Then the Windows user holds down the Ctrl key on the keyboard, the left mouse button clicks the search,Mac user holds down the Command key on the keyboard, and the left mouse button clicks search,PyCharm, which automatically jumps to the re module of Python. Here, you will see that our commonly used regular expression methods, whether findall or search or sub or match, are all written like this:

_ compile (pattern, flag). Corresponding method (string)

For example:

Def findall (pattern, string, flags=0): "" Return a list of all non-overlapping matches in the string. If one or more capturing groups are present in the pattern, return a list of groups; this will be a list of tuples if the pattern has more than one group. Empty matches are included in the result. "" Return _ compile (pattern, flags) .findall (string)

As shown in the following figure:

Then let's take a look at compile:

Def compile (pattern, flags=0): "Compile a regular expression pattern, returning a Pattern object." Return _ compile (pattern, flags)

As shown in the following figure:

Do you see the problem?

Our commonly used regular expression methods already have their own compile!

There is no need to re.compile and then call the regular expression method.

At this point, someone may retort:

If I have 1 million strings and use a regular expression to match, then I can write the code like this:

Texts = [list of a million strings] pattern = re.compile ('regular expression') for text in texts: pattern.search (text)

At this point, re.compile only executes once, and if you write code like this:

Texts = [list of a million strings] for text in texts: re.search ('regular expression', text)

It is equivalent to executing re.compile on the same regular expression 1 million times at the bottom.

Talk is cheap, show me the code.

Let's look at the source code. The regular expression re.compile calls _ compile, so let's look at the source code of _ compile, as shown in the following figure:

The code in the red box shows that _ compile has its own cache. It automatically stores up to 512 Key consisting of type (pattern), pattern, flags). As long as it is the same regular expression and the same flag, the cache will be read directly the second time when _ compile is called twice.

To sum up, please stop calling re.compile manually, which is a bad habit brought from other languages (yes, I'm talking about Java).

The above is all the content of the article "Why Don't use re.compile in Python". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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