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About python Tips

The difference between the two lists

We now have two lists models and object_detections

models = ['fastRCNN', 'YOLO', 'mask-rcnn', 'deeplab', 'FCN']

object_detections = ['fastRCNN', 'YOLO', 'mask-rcnn']

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We want to find some models , That is to say models and object_detections That is, this element exists in models There is no such thing as object_detections

models_set = set(models)

object_detections_set = set(object_detections)

segmentation = list(models_set.symmetric_difference(object_detections_set))

print(segmentation)

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Calculation python The amount of memory occupied by the object

About any data structure （ As listing 、 Dictionary or any object ） To store values or records , Check the size of the memory occupied by the data structure . It is a good practice to view how much memory the data structure uses sys.getsizeof Returns the size of the object , The unit is byte .

import sys

object_detections = ['fastRCNN', 'YOLO', 'mask-rcnn']

print("size of list = ",sys.getsizeof(object_detections))

#Memory: 4076 kilobyte(s)

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List to heavy

In most cases , Requirements remove repeating elements from the list . Usually we use them set This automatic de duplication confluence , stay set You are not allowed to have repeated elements in .

listNumbers = [1,2,2,5,5,5,6,7,8]

print("Original= ", listNumbers)

listNumbers = list(set(listNumbers))

print("After removing duplicate= ", listNumbers)

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Original=  [1, 2, 2, 5, 5, 5, 6, 7, 8]

After removing duplicate=  [1, 2, 5, 6, 7, 8]

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How to effectively compare two lists

Usually we need to compare whether the two lists are the same ,

from collections import Counter

one = [1, 5, 3, 7, 9]

two = [9, 1, 3, 5, 7]

print(" Compare whether the two lists are the same ", Counter(one) == Counter(two))

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The object is hashable Be able to use collections.Counter 

Can also use sorted() Stop sorting and see if it's the same

The detection list contains only one element

Check whether a list can contain only one element , Here's a little trick , That is to calculate the number of elements presented , Application count Can it be the same length as the list , If the same , To clarify that all elements in the list are divergent .

a = [3, 3, 3,3]

print("All element are duplicate in listOne", a.count(a[0]) == len(a))

b = [3, 3, 3,2]

print("All element are duplicate in listTwo", b.count(b[0]) == len(b))

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It takes time to calculate the function

Usually we need to understand how long our functions take , To weigh the performance of a function .

import time startTime = time.time() 

# Your code

endTime = time.time() 

totalTime = endTime - startTime 

print("Total time required to execute code is= ", totalTime)