Day06 list job

list

One 、 List slice

1.1 section - Get some elements
The result of slicing is a list

 grammar ： list [ Start subscript ： End subscript ： step ]
 explain ：
 Start subscript     -    Subscript value （0 Starting and -1 Anything at the beginning ）; It is the starting point for determining the effective range of slices , You can get it. 
：         -    Fixed writing 
 End subscript     -    Subscript value （0 Starting and -1 Anything at the beginning ）; Determine the end point of the slice effective range , Can't get 
 step       -     1) Determine the direction of the slice ( The direction corresponding to the step size must be consistent with the direction from start to end )
               2) How to get elements （ Take one by one or jump ）

 Be careful : The valid range of slices is ：[ Start subscript , End subscript )

games = [' Glory of Kings ', ' Game for Peace ', ' Protogod ', ' , ', ' Crossing the line of fire ', ' Tribal conflict ', ' Red Alert ', ' Contra ']
print(games[1:5:1])             # [' Game for Peace ', ' Protogod ', ' , ', ' Crossing the line of fire ']
print(games[1:-1:1])            # [' Game for Peace ', ' Protogod ', ' , ', ' Crossing the line of fire ', ' Tribal conflict ', ' Red Alert ']
print(games[3:-1:-1])           # []
print(games[-1:-5:1])           # []
print(games[0:-3:2])            # [' Glory of Kings ', ' Protogod ', ' Crossing the line of fire ']
print(games[-1:2:-2])           # [' Contra ', ' Tribal conflict ', ' , ']
print(games[2:-1:1])            # [ Protogod ', ' , ', ' Crossing the line of fire ', ' Tribal conflict ', ' Red Alert ']

1.2 Omit step size

list [ Start subscript ： End subscript ] == [ Start subscript ： End subscript ：1]
Omit step size , Step size is 1

games = [' Glory of Kings ', ' Game for Peace ', ' Biochemical crisis ', ' Protogod ', ' , ', ' Crossing the line of fire ', ' Tribal conflict ', ' Red Alert ', ' Contra ']
print(games[2:-2])          # [' Protogod ', ' , ', ' Crossing the line of fire ', ' Tribal conflict ']

1.3 Omit start subscript

list [： End subscript ： step ] / list [: End subscript ]
Omit start subscript , If the step size is positive , Start with the first element and take it back ; If the step size is negative , Start with the last element and move forward

games = [' Glory of Kings ', ' Game for Peace ', ' Biochemical crisis ', ' Protogod ', ' , ', ' Crossing the line of fire ', ' Tribal conflict ', ' Red Alert ', ' Contra ']
print(games[:-3])           # [' Glory of Kings ', ' Game for Peace ', ' Biochemical crisis ', ' Protogod ', ' , ', ' Crossing the line of fire ']
print(games[:3:-1])         # [' Contra ', ' Red Alert ', ' Tribal conflict ', ' Crossing the line of fire ', ' , ']

1.4 Omit the closing subscript

list [ Start subscript ：: step ] # Omit the closing subscript
list [ Start subscript ：] # Omit the end mark and step
Omit the closing subscript ： If the step size is positive , Take the last element from the beginning subscript ; If the step size is negative , Take the first element from the starting subscript

games = [' Glory of Kings ', ' Game for Peace ', ' Biochemical crisis ', ' Protogod ', ' , ', ' Crossing the line of fire ', ' Tribal conflict ', ' Red Alert ', ' Contra ']
print(games[1:])            # [' Game for Peace ', ' Biochemical crisis ', ' Protogod ', ' , ', ' Crossing the line of fire ', ' Tribal conflict ', ' Red Alert ', ' Contra ']
print(games[3::2])          # [' Protogod ', ' Crossing the line of fire ', ' Red Alert ']
print(games[-2::-1])        # [' Red Alert ', ' Tribal conflict ', ' Crossing the line of fire ', ' , ', ' Protogod ', ' Biochemical crisis ', ' Game for Peace ', ' Glory of Kings ']

1.5 Together province

list [：: step ] # If the step size is positive , From the first element to the last element ; If the step size is negative , From the last element to the first element
list [:] # Take the whole list

print(games[::-1])          # [' Contra ', ' Red Alert ', ' Tribal conflict ', ' Crossing the line of fire ', ' , ', ' Protogod ', ' Biochemical crisis ', ' Game for Peace ', ' Glory of Kings ']
print(games[::2])           # [' Glory of Kings ', ' Biochemical crisis ', ' , ', ' Tribal conflict ', ' Contra ']
print(games[:])             # [' Glory of Kings ', ' Game for Peace ', ' Biochemical crisis ', ' Protogod ', ' , ', ' Crossing the line of fire ', ' Tribal conflict ', ' Red Alert ', ' Contra ']

print('abcdef'[1:])
print('abcdef'[::2])

Two 、 Deletion and modification

1.1 Delete - Delete list elements ( Reduce the number of list elements )
teleplays = [‘ List of reed {langya} ’, ‘ Daqin ’, ‘ The temptation of home ’, ‘ Kangxi Dynasty ’, ‘ Two Broke Girls ’, ‘ Strong-arm reaction ’, ‘ The big bang theory ’, ‘ Journey to the west ’]

1. del list [ Subscript ] - Delete the element corresponding to the specified subscript in the list
   Be careful ： Subscript cannot be out of bounds

del teleplays[2]
print(teleplays)    # [' List of reed {langya} ', ' Daqin ', ' Kangxi Dynasty ', ' Two Broke Girls ', ' Strong-arm reaction ', ' The big bang theory ', ' Journey to the west ']
del teleplays[-2]
print(teleplays)    # [' List of reed {langya} ', ' Daqin ', ' Kangxi Dynasty ', ' Two Broke Girls ', ' Strong-arm reaction ', ' Journey to the west ']

2. list .remove( Elements ) - Deletes the specified element in the list
   Be careful ：a. If the element does not exist , Will report a mistake
   b. If the element has more than one , Delete only the first

teleplays.remove(' List of reed {langya} ')
print(teleplays)        # [' Daqin ', ' Kangxi Dynasty ', ' Two Broke Girls ', ' Strong-arm reaction ', ' Journey to the west ']
teleplays.remove(' The white snake ')     # ValueError: list.remove(x): x not in list
nums = [10, 20, 30, 20, 10, 20]
nums.remove(20)
print(nums)     # [10, 30, 20, 10, 20]

3. list . pop() - Take out the last element of the list
   list .pop( Subscript ) - Take out the element corresponding to the specified subscript in the list

teleplays = [' List of reed {langya} ', ' Daqin ', ' The temptation of home ', ' Kangxi Dynasty ', ' Two Broke Girls ', ' Strong-arm reaction ', ' The big bang theory ', ' Journey to the west ']
del_item = teleplays.pop()
print(teleplays)
print(del_item)    #  Deleted ' Journey to the west '

4). list .clear() - List is empty

teleplays = [' List of reed {langya} ', ' Daqin ', ' The temptation of home ', ' Kangxi Dynasty ', ' Two Broke Girls ', ' Strong-arm reaction ', ' The big bang theory ', ' Journey to the west ']
teleplays.clear()
print(teleplays)
teleplays = [' List of reed {langya} ', ' Daqin ', ' The temptation of home ', ' Kangxi Dynasty ', ' Two Broke Girls ', ' Strong-arm reaction ', ' The big bang theory ', ' Journey to the west ']
print(teleplays)
teleplays = []
print(teleplays)

2. Change - Modify the value of an element
   list [ Subscript ] = value - Modify the element corresponding to the specified subscript in the list to the specified value

teleplays = [' List of reed {langya} ', ' Daqin ', ' The temptation of home ', ' Kangxi Dynasty ', ' Two Broke Girls ', ' Strong-arm reaction ', ' The big bang theory ', ' Journey to the west ']
print(teleplays)
teleplays[0] = ' Celebrate more than '
print(teleplays)

practice ： Will be lower than 60 All the scores are changed to 0 branch

Method 1 ：

scores = [90, 45, 56, 89, 76, 56, 92, 45, 30, 59, 67, 70]
for index in range(len(scores)):
    if scores[index] < 60:
        scores[index] = 0
print(scores)

Method 2 ：

for index, item in enumerate(scores):
    if item < 60:
        scores[index] = 0
print(scores)

Method 3 ：

scores = [90, 45, 56, 89, 76, 56, 92, 45, 30, 59, 67, 70]
new_scores = []
for item in scores:
    if item < 60:
        new_scores.append(0)
        continue
    new_scores.append(item)
print(new_scores)

3、 ... and 、 List related operations

1. Numeric operators ：+、*
   list 1 + list 2 – Will list 1 And list 2 Merge into a new list
   list 1 * N / N * list 1 – take N A list 1 Merge to produce a new list

print([1, 2, 3]+[10, 20, 30])

list1 = [100, 200]
list2 = [1000, 2000]
print(list1 + list2, list1)
print(list1 * 3)        # [100, 200, 100, 200, 100, 200]

2. Comparison operator ：、!=、>、<、>=、<=
   1)、!=

print([1, 2, 3] == [1, 2, 3])
print([1, 2, 3] == [1, 3, 2])
print({
    1, 2, 3} == {
    1, 3, 2})

​ 2) list 1 > (<、>=、<=) list 2
The principle of comparing the size of two lists ： Compare the size of the first pair of unequal elements ( The elements with the same subscript in two lists are a pair , This subscript is 0 The starting subscript )

print([1, 200, 300, 400, 500] > [10, 2])        # False
print([11, 0, 0, 0] > [10, 2])      # True

3. in and not in
   Elements in list - Determine if a specified element exists in the list
   Elements not in list - Determine whether the specified element does not exist in the list

print(10 in [10, 20, 30])       # True
print([10, 20] in [10, 20, 30])   # False
print([10, 20] in [[10, 20], 30])   # True

practice ： Judge whether the score is 100 Points or 0 Points or 60

score = 89
if score == 100 or score == 0 or score == 60:
    print(' Special values ')

if score in [0, 60, 100]:
    print(' Special values ')


v = 34
if type(v) == int or type(v) == float or type(v) == complex or type(v) == bool:
    print(' Numbers ')
else:
    print(' Not numbers ')

if type(v) in [int, float, complex, bool]:
    print(' Numbers ')
else:
    print(' Not numbers ')

5、 ... and 、 Correlation functions and methods

1. List related methods ：copy、count、index、reverse、sort
   1) list .count( Elements ) - Count the number of specified elements in the list

nums = [10, 20, 30, 4, 10, 20, 10, 10]
print(nums.count(10))    # 4
print(nums.count(4))     # 1
print(nums.count(100))   # 0

2. list .index( Elements ) - Get the subscript of the element that appears in the list for the first time ( The subscript is 0 Starting subscript value )

print(nums.index(10))   # 0
print(nums.index(20))   # 1
print(nums.index(4))    # 3
# print(nums.index(100)) # ValueError: 100 is not in list( Not found in the list 100)

3. . list .reverse() - In reverse order

nums = [10, 20, 5, 2, 100]
nums.reverse()
print(nums)     # [2, 5, 20, 10]

4). list .sort() - Sort the elements in the list from small to large
list .sort(reverse=True) - Sort the elements in the list from large to small

nums = [10, 20, 5, 2, 100]
nums.sort()
print(nums)     # [2, 5, 10, 20, 100]


nums = [10, 20, 5, 2, 100]
nums.sort(reverse=True)
print(nums)     # [100, 20, 10, 5, 2]

5. list .copy() - Copying the list produces a new list with exactly the same elements

list1 = [10, 20, 30]
print(list1)     # [10, 20, 30]
list2 = list1
print(list2)     # [10, 20, 30]
list3 = list1.copy()
print(list3)     # [10, 20, 30]

list1.append(100)
print(list2)    # [10, 20, 30, 100]
print(list1)    # [10, 20, 30, 100]
print(list3)    # [10, 20, 30]

List job

1. Know a list of numbers , Find the central element of the list .

nums = [12, 32, 73, 5, 83, 66, 52]
count = len(nums)
if count % 2:
    print(nums[count//2])
else:
    index = count//2
    print(nums[index//2-1], nums[index//2])

2. Know a list of numbers , Sum all elements .

nums = [2, 23, 5, 67, 87, 76, 9, 4]
sum1 = 0
for item in nums:
    sum1 += item
print(sum1)

3. Know a list of numbers , Output all odd subscript elements .

nums = [2, 23, 5, 67, 87, 76, 9, 4]
print(nums[1::2])

4. Know a list of numbers , Output all elements , Elements with odd values .

nums = [2, 23, 5, 67, 87, 76, 9, 4]
for item in nums:
    if item % 2 == 1:
        print(item)

5. Know a list of numbers , Multiply all elements by two .

for example ：nums = [1, 2, 3, 4] —> nums = [2, 4, 6, 8]

nums = [2, 23, 5, 67, 87, 76, 9, 4]
new_nums = []
for item in nums:
    new_nums.append(item * 2)
print(new_nums)

6. One length is 10 A list of , There are... In the array 10 Personal name , Ask to get rid of the duplicate

for example :names = [‘ Zhang San ’, ‘ Li Si ’, ‘ rhubarb ’, ‘ rhubarb ’, ‘ Zhang San ’, ‘ Zhang San ’, ‘ Zhang San ’] -> names = [‘ Zhang San ’, ‘ Li Si ’, ‘ rhubarb ’]

names = [2, 2, 5, 87, 87, 76, 7, 76]
new_names = []
for name in names:
    if name not in new_names:
        new_names.append(name)
print(new_names)			# [2, 5, 87, 76, 7]

7. Use a list to save all the scores of a program , Find the average score ( Remove one of the highest scores , Remove a minimum score , Find the final score )

scores = [82, 83, 85, 77, 87, 76, 90, 84]
max_score = min_score = scores[0]
sum1 = 0
for item in scores:
    if item > max_score:
        max_score = item
    elif item < min_score:
        min_score = item
    sum1 += item
print((sum1- max_score - min_score) / (len(scores) - 2))

8. There are two lists A and B, Use list C To get the common elements in the two lists

for example : A = [1, ‘a’, 4, 90] B = [‘a’, 8, ‘j’, 1] --> C = [1, ‘a’]

a = [12, 32, 73, 5, 83, 66, 52]
b = [82, 83, 85, 77, 87, 76, 90, 84]
c = []
for i in a:
    if i in b:
        c.append(i)
print(c)

9. There's a list of numbers , Get the maximum value in this list .( Be careful : Out of commission max function )

for example : nums = [19, 89, 90, 600, 1] —> 600

nums = [85, 77, 87, 76, 90, 84]
max_value = nums[0]
for item in nums[1:]:
    if item > max_value:
        max_value = item
print(max_value)

10. Get the most frequent element in the list

for example ：nums = [1, 2, 3,1,4,2,1,3,7,3,3] —> Print :3

nums = [2, 1, 3, 2, 1, 6, 8, 5, 3, 2, 1, 5, 1, 3]
count = 0
max = []
for x in nums:
  if x in max:
    continue
  c = nums.count(x)
  if c > count:
    max.clear()
    count = c
    max.append(x)
  elif c == count:
    max.append(x)
print(max)