What is sys in python

sys.argv[] To put it bluntly, it is a bridge to obtain parameters from outside the program. This "external" is very critical, so those who try to explain its function from the code have never understood it.

Because we can get multiple parameters from the outside, what we get is a list. That is to say, sys.argv can actually be regarded as a list, so we can use [] to extract the parameters. element. The first element is the program itself, followed by externally given parameters.

Below we illustrate its usage through the running results of a very simple test.py program.

Save test.py in the root directory of the c drive.

Find 'Run' in the program->Click->Enter "cmd"->Enter key to enter the console command window (as shown below), first enter cd c:\ (the function is to Change the command path to the root directory of drive c), then enter test.py to run the program we just wrote:

The result is C:\test.py, which is 0 refers to the code (that is, this .py program) itself.

Then we change the 0 in the code to 1:

a=sys.argv[1]

After saving, run it from the console window. This time we add a parameter and enter: test.py what

The result obtained is what we entered as the parameter. Do you begin to understand when you see this?

Then let’s modify the code again:

a=sys.argv[2：]

After saving, run the program from the console window. This time add a few more parameters, separated by spaces:

test.py a b c d e f

The result obtained is ['b', 'c', 'd', 'e', ​​'f']

You should be enlightened now. Sys.argv[ ] is actually a list, and the items inside are parameters input by the user. The key is to understand that these parameters are input from outside the program, rather than somewhere in the code itself. If you want to see its effect, you should The program is saved, and the program can be run externally and given parameters.

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