1. Python self-study diary (loop, list)

Ternary operator 

Syntax: x if condition else y  

Example

small = x if < x else y

assert

When the condition following this keyword is false, the program automatically crashes and throws an AssertionError exception. Generally used for inspection.

Example  

assert 3>4

While

grammar 

 while condition:

    loop body

for loop

grammar  

for target in expression

    loop body

range（）

grammar 

range([strart,] stop[,step=1]) 

1. Indicates that this BIF has three parameters, two of which are enclosed in square brackets to indicate that these two parameters are optional.

2.step = 1 means the default value of the third parameter is 1.

3. The role of the range BIF is to generate a sequence of numbers starting from the value of the start parameter and ending with the value of the stop parameter.

for i in range(5):
   print(i)

The output is 0 1 2 3 4

for i in range(2,9):
   print(i)

The output is 2 3 4 5 6 7 8

for i in range(1,10,2):
   print(i)

The output is 1 3 5 7 9 

break 和 continue

break out of the loop 

bingo = 'I love Mario'
answer = input('Please enter the sentence that Little Turtle wants to hear most:')

while True:
    if answer == bingo:
        break
    answer = input('Sorry, wrong, please re-enter (the answer is correct to exit the game):')

print('Ouch, handsome~')
print('You are really a roundworm in Mario's stomach ^_^')

continue to terminate the current cycle and start the next cycle

for i in range(10):
    if i%2 != 0:
        print(i)
        continue
    i += 2
    print(i)

list (an array of hormones typed)

1. Create a normal list

member = ["1","2","3"]
member

2. Create a Mixed List

mix = [1,"text",3.14,[1,2,3]]

3. Create an empty list

empty = []

add element to list

append()

Can't add member.append("5","6") like this

member = ["1","2","3"]
member.append("4")
member

extend()

Extend a list with another list member.extend(["5","6"])

member = ["1","2","3"]
member.extend(["5","6"])
member

insert()

Two parameters The first parameter represents the position in the list The second parameter represents the position of the first parameter to insert an element (that is, the element name)

member = ["1","2","3"]
member.insert(0,"0")
member

swap element position

member = ["4","2","3","1"]
temp = member[0]
member[0] = member[3]
member[3] = temp
member

remove element from list

1.remove() The parameter is the element name

member = ["4","2","3","1"]
member.remove("2")

If there is no such element, an error is reported

2. del statement

member = ["4","2","3","1"]
del member[1]
member

If del member then delete the entire list

member = ["4","2","3","1"]
del member
member

3. pop() removes the last element and returns (assignable)

member = ["4","2","3","1"]
member.pop()

Addable parameters (position number)

member = ["4","2","3","1"]
member.pop(1)
member

4. Fragmentation (assignable)

member = ["4","2","3","1"]
member[1:3]
member

 

back 2 3 

It can be abbreviated. No number before the colon means to start from the front. Similarly, no number after the colon means to get to the end. Copy the entire list without writing on both sides (assignable)

member = ["4","2","3","1","5","6"]
member[:3]
member[1:]

List of common operators

1. Compare

Compare the first item of an array

2. The + sign must be of the same type 

3. Example of copying the list 3 times with * 

list = [123,456]
list*3

4. = assignment can be combined with *

list = [123，456]
list *= 3
list

5. Membership operator

return true or false 

list = [123，456]
"123" in list
"123" not in list
"文字" in list
"文字" not in list

Determine the elements of a list in a list

list = [012,["text","text1"],4566]
"文字" in list[1]

access the value of the list in the list

list = [012,["text","text1"],4566]
list[1][1]

List type built-in function BIF

you(list)

1.count counts the number of times the parameter appears in the list

list[123,123,456,789,8,,78,87,8745,64678,74,685,1321654,8,74,564,89,7,98,74,454,654,8,7,1]
list.count(123)

2.index returns the position in the list, three parameters (element, start, end)

list[123,123,456,789,8,,78,87,8745,64678,74,685,1321654,8,74,564,89,7,98,74,454,654,8,7,1]
list.index(123)

list[123,123,456,789,8,,78,87,8745,64678,74,685,1321654,8,74,564,89,7,98,74,454,654,8,7,1]
list.count(123,0,6)

3.reverse flips the entire list

list[123,123,456,789,8,,78,87,8745,64678,74,685,1321654,8,74,564,89,7,98,74,454,654,8,7,1]
list.reverse()
list

4 sort is used to specify that the list is sorted from small to large by default

list = [1,3,2,5,8,78,46,4,54,531,3,48,]
list.sort()
list

Sort from largest to smallest 

list = [1,3,2,5,8,78,46,4,54,531,3,48,]
list.sort(reverse.true)
list