How to use the sys module to obtain command line parameters in Python 2.x

As a flexible and easy-to-use programming language, Python provides many modules for operating systems and command lines. One of them is the sys module, which provides us with some tools to handle command line parameters. In this article, we will learn how to get command line arguments in Python 2.x using the sys module.

First of all, we need to understand that the sys module is part of the Python standard library, so there is no need to install additional packages. We just need to import the sys module at the beginning of the code:

import sys

In Python, sys.argv is a list containing command line arguments. Among them, sys.argv[0] is the name of the script itself, while the other elements are the parameters provided when executing the script from the command line. For example, if we run the following command:

python script.py arg1 arg2

then the value of sys.argv will be:

['script.py', 'arg1', 'arg2']

We can access these parameters by iterating over sys.argv. Here is a simple sample code:

import sys

# 遍历并打印命令行参数
for arg in sys.argv:
    print(arg)

When we run the above code and provide some command line parameters, it will print out these parameters. For example, if we run the following command:

python script.py hello world

then the output will be:

script.py
hello
world

Another useful feature is to check the number of command line arguments through sys.argv. We can use the len function to get the length of sys.argv and then further process these parameters. The following sample code demonstrates how to verify that the number of command line arguments is correct:

import sys

# 确保至少有两个参数
if len(sys.argv) < 3:
    print("请提供至少两个参数")
    sys.exit()

# 打印所有参数
for arg in sys.argv:
    print(arg)

When we provide less than two arguments, it will output an error message and exit the script. Otherwise, it prints all parameters.

In the sys module of Python 2.x, there are some other functions that can be used to process command line parameters. For example, sys.argv[0] can obtain the full path name of the executed script. In addition, the slicing operation of sys.argv can be used to process specific command line parameters. We can use sys.argv[1:] to get all arguments except the script name and use them for further processing.

It should be noted that when using the sys module to handle command line parameters, we should follow some best practices. First, we should do some input validation in the code to ensure that the correct number and format of parameters are provided. Secondly, we should provide default values ​​for optional parameters to avoid exceptions when parameters are not provided.

In short, the sys module provides us with a convenient way to obtain and process command line parameters. Not only can it help us implement some basic operations, but it can also be used for more complex applications. I hope the introduction in this article can help you use the sys module to process command line parameters in Python 2.x.

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