[] is a bridge to get parameters from outside the program, this "outside" is very critical, so those who try to explain it from the code to explain the role of the explanation has not been clear. Because we can take more than one parameter from outside the program, we get a list, which can actually be seen as a list, so we can use [] to extract its elements. The first element is the program itself, followed by the externally given parameters.
as below
import sys a = [0] print(a)
Save and run as follows
The result obtained is that this is what 0 means by the code (i.e. this .py program) itself.
Then we change 0 to 1 in the code :
import sys a = [1] print(a)
runs and outputs the parameters we passed in, so [] is what gets the parameters we passed in from the console
Next, let's change the code a bit to get the full parameters of the inputs
import sys a = [1:] print(a)
The results obtained are ['11', '22', '33', '44', '55']
In fact, it is a list of items for the user input parameters, the key is to understand that this parameter is input from outside the program, rather than the code itself somewhere, to see the effect of it should save the program, from the outside to run the program and give parameters.
P.S. Python reads the parameters of a command line using the
#!/usr/bin/python import sys print "Script Name:", [0]
The above code prints out the name of the executable program, together with the len() function, you can know how many arguments are input to the instruction. Here is how to use len() function to print out the input parameters.
#!/usr/bin/python import sys n = len() for i in range(1, n): print [i]
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