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Detailed explanation of three methods of Python string concatenation and their efficiency and applicable scenarios

高洛峰Original: 2016-10-17 16:53:241633browse

Python string concatenation methods generally have the following three methods:

Method 1: Connect directly through the plus (+) operator

website = &#39;python&#39; + &#39;tab&#39; + &#39;.com&#39;

Method 2: join method

listStr = [&#39;python&#39;, &#39;tab&#39;, &#39;.com&#39;] 
website = &#39;&#39;.join(listStr)

Method 3 : Replace

website = &#39;%s%s%s&#39; % (&#39;python&#39;, &#39;tab&#39;, &#39;.com&#39;)

Let’s talk about the differences between the three methods

Method 1 is simple and direct to use, but many people on the Internet say that this method is inefficient

The reason why it is used in python + The inefficiency of string concatenation is because strings in python are immutable types. When using + to connect two strings, a new string will be generated. To generate a new string, you need to apply for memory again. When continuous When there are many strings to be added (a+b+c+d+e+f+...), low efficiency is inevitable

Method 2 is slightly complicated to use, but when concatenating multiple characters High efficiency, there will only be one memory application. And if you are connecting the characters of the list, this method must be the first choice

Method 3: String formatting, this method is very commonly used, I also recommend this method

Use it below Experiment to illustrate the efficiency of string concatenation.

比较对象：加号连接 VS join连接
python版本： python2.7
系统环境：CentOS

Experiment 1:

# -*- coding: utf-8 -*-
from time import time
def method1():
    t = time()
    for i in xrange(100000):
        s = &#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;
    print time() - t
def method2():
    t = time()
    for i in xrange(100000):
        s = &#39;&#39;.join([&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;])
    print time() -t
method1()
method2()

Result:

0.641695976257
0.341440916061

Experiment 2:

# -*- coding: utf-8 -*-
from time import time
def method1():
    t = time()
    for i in xrange(100000):
        s = &#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;+&#39;pythontab&#39;
    print time() - t
def method2():
    t = time()
    for i in xrange(100000):
        s = &#39;&#39;.join([&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;,&#39;pythontab&#39;])
    print time() -t
method1()
method2()

Result:

0.0265691280365
0.0522091388702

The above two The experiments produced completely different results. The only difference between the two experiments was the number of string connections.

Conclusion: The low efficiency of plus sign connection occurs when multiple string connections are performed continuously. If the number of connections is small, the efficiency of plus sign connection is higher than that of join connection

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