Summary of common operations on lists, strings, and dictionaries in Python

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The list operation is as follows:

a = ["haha","xixi","baba "]

Add: a.append[gg]

a.insert[1,gg] At the subscript 1, add gg

Delete: a. remove(haha) deletes the first matching haha ​​from left to right in the list

del a.[0] deletes the value corresponding to the subscript 0
a.pop(0) in brackets If the content is not written, the last one will be deleted by default. If it is written, the content corresponding to the subscript will be deleted.

Change: a.[0] = "gg"

Check: a[0]

a.index("haha") displays the subscript of the first matching haha ​​from left to right.
a.count("haha") displays the total number of haha ​​in the list.
a. clear() clears the list a

Quickly traverses the contents of the list, removes subscripts, and prints them together.

enumerate(a) takes out each subscript and subscript content of the list and puts it into an array, so it can be traversed using a for loop.

a = ["haha","xixi","baba"]
for index,data in enumerate(a):print(index,":",data)

Result:

0 : haha
1 : xixi
2 : baba

##Key words:

a.copy() shallow copy, such as a = ["haha","xixi",["yan","liu"],"baba"]

b = a.copy()

Modify the content outside a, b will not change with it!

Modify the list content in a ["yan", "liu"], b will change accordingly~~

Reason: In fact, the list in list a ["yan", "liu" "] exists alone in the memory. a just writes this memory pointer here. ["yan", "liu"] It is independent.

Simple use: Create a common account, that is, the outer layer is independent and the inner layer list is shared.

import copy

b = copy.deepcopy(a) deep, complete copy, b completely independent. But use sparingly. Because a separate memory space will be opened up. If the list a is large, this will consume a lot of memory.

String operations:

name = "The name is {name}, the age is {age}"

print(name. capitalize()) #Capitalize the first letter
print(name.center(50,"-")) #Add 25 "-" to the left and right
print(name.endswith("an")) #Judge whether it is Ending with "an"
print(name.find("a")) #The subscript of the first "a" found from left to right
print(name.format(name="yan" ,age="24")) #Transform the content in the string {}

Dictionary operation:

Dictionary to obtain the value Method:

a = {"yan":123,"liu":456}

print(a["yan"]) #Method 1, if the key does not exist, an error will be reported
print (a.get("yanada")) #Method 2, if ket does not exist, return None

a.keys() #Get key

a.values() #Get value

*** serdefault usage:

a.setdefault("yan",789)

print(a)
{ 'liu': 456, 'yan': 123}
a.setdefault("wang",789)
print(a)
{'yan': 123, 'liu': 456, 'wang ': 789}

First go to the dictionary to find the key value. If it is found, it will return its corresponding value. If it is not found, it proves that it does not exist. Then add a new key value and assign the value. This way, you can add When adding the contents of the dictionary, it is used to prevent the key values ​​from being the same and the new addition being unsuccessful. Instead, the value corresponding to the original key should be deleted.

*** Update usage:

a = {"yan":123,"liu":456}

b = {"yan":666,"haha":888}
a. update(b)
print(a)
{'yan': 666, 'haha': 888, 'liu': 456}

Pass b as a parameter to the update function, Merge with a, if the key value is the same, b will prevail, and a’s will be updated

items usage:

Change the dictionary into a list, where the list content---key and Value forms a tuple, the key subscript is 0, and the value subscript is 1

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