Detailed introduction to three methods of using Python string connection and their efficiency and applicable scenarios-Python Tutorial-php.cn

Detailed introduction to three methods of using Python string connection and their efficiency and applicable scenarios

高洛峰

Release： 2017-03-19 15:27:16

Original

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python There are generally three ways to connect strings:

Method 1: Directly through the plus sign (+)operatorConnection

website = 'python' + 'tab' + '.com'

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Method 2: join method

listStr = ['python', 'tab', '.com'] 
website = ''.join(listStr)

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Method 3: Replacement

website = '%s%s%s' % ('python', 'tab', '.com')

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Let’s talk about the differences between the three methods

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

The reason why using + for string connection in python is inefficient 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 there are many strings that are continuously added (a+b+c+d+e+f+.. .), low efficiency is inevitable

Method 2 is slightly complicated to use, but it is efficient when connecting multiple characters, and there will only be one memory application. And if you are connecting characters in a list, this method must be the first choice

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

The following experiments are used 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

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Experiment one:

# -*- coding: utf-8 -*-
from time import time
def method1():
    t = time()
    for i in xrange(100000):
        s = 'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'+'pythontab'
    print time() - t
def method2():
    t = time()
    for i in xrange(100000):
        s = ''.join(['pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab','pythontab'])
    print time() -t
method1()
method2()

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Result:

0.641695976257
0.341440916061

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Experiment two:

# -*- coding: utf-8 -*-
from time import time
def method1():
    t = time()
    for i in xrange(100000):
        s = 'pythontab'+'pythontab'+'pythontab'+'pythontab'
    print time() - t
def method2():
    t = time()
    for i in xrange(100000):
        s = ''.join(['pythontab','pythontab','pythontab','pythontab'])
    print time() -t
method1()
method2()

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Result:

0.0265691280365
0.0522091388702

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The above two experiments appeared Completely different results were obtained. The only difference between the two experiments is: 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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