Python-week2, week 2 (based on Python3.0 or above ),

Python-week2, week 2 (based on Python3.0 or above ),
1, list

We can use variables to store data, but when there are a lot of data, there will be many limitations when using variables, so the list is used at this time. The list is separated by commas (,) for each element in brackets. For example, [1, 2, 3] is a list. You can assign this list to a variable name. Next let's take a look at how to query, add, modify, and delete a list.

Query the list:

If you want to print a parameter in the list, you can use the subscript (location) parameter of the List to call it out.

1 name = ["Zhao", "Qian", "Sun", "Li", "Zhou", "Wu"] 2 print (name [1])

In this way, we printed the word "money". Note that the position in the program starts from 0.

If you want to print multiple elements, you can use the slice method:

1 name = ["Zhao", "Qian", "Sun", "Li", "Zhou", "Wu"] 2 3 print (name [0: 3])

Note that the slice does not contain the position at the end. If the position above is not 3, "Li" is not printed ". Slice you still have many cutting methods, such as cutting from the center, cutting from the back, continuously cutting or jumping. Here we will not give an example one by one, because I am a little lazy 0.0 ///. Note that we write the position parameter from left to right, that is, the second number is greater than the first number. [-1:-3] is incorrect, it should be [-3:-1].

What else do we know about an element and want to check its position in the list? We can use the index method.

1 name = ["Zhao", "Qian", "Sun", "Li", "Zhou", "Wu"] 2 3 print (name. index ("Li "))

How many times has it appeared in the list? Use the count method (replace the index with count ).

List addition:

If we want to add an element to the list, we use the append method. Append is append, that is, append at the end.

1 name = ["Zhao", "Qian", "Sun", "Li", "Zhou", "Wu"] 2 3 name. append ("yellow") 4 print (name)

If the value is added at a specified position, the insert method is used. For example, add in position 3.

1 name = ["Zhao", "Qian", "Sun", "Li", "Zhou", "Wu"] 2 3 name. insert (3, "yellow") 4 print (name)

Or we can convert it into another list and use extend to merge it. This is called an extension.

1 name = ["Zhao", "Qian", "Sun", "Li", "Zhou", "Wu"] 2 name2 = ["yellow"] 3 name. extend (name2) 4 print (name)

List modification:

Next is the modification of the list, which is easy to understand.

1 name = ["Zhao", "Qian", "Sun", "Li", "Zhou ", "Wu"] 2 name [3] = "yellow" 3 print (name)

 

Delete A list:

You can use the del, remove, and pop methods to delete a file.

1 name = ["Zhao", "Qian", "Sun", "Li", "Zhou", "Wu"] 2 del name [3] 3 print (name) 4 5 name = ["Zhao", "Qian", "Sun", "Li", "Zhou", "Wu"] 6 name. remove ("Li") 7 print (name) 8 9 name = ["Zhao", "Qian", "Sun", "Li", "Zhou ", "Wu"] 10 name. pop () # If no parameter exists, the last 11 print (name) is deleted by default)

Other methods of the list:

There are still some syntaxes In the list. Let's introduce their functions one by one. Reverse (reverse), sort (sort ),.... Knock on the blackboard .. Focus on copy ).

1 name = ["a Zhao", "f Qian", "e sun", "d li", "c weeks", "B Wu"] 2 name. sort () 3 print (name) 4 name. reverse () 5 print (name)

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