Detailed graphic explanation of Python set type (list tuple dict set generator)-Python Tutorial-php.cn

PythonThe built-in collection types include list, tuple, set, and dict.

List list: Looks like an array, but is more powerful than an array and supports functions such as indexing, slicing, search, and addition.

Tuple tuple: The function is similar to the list, but once generated, the length and elements are not variable (the elements of the elements are still variable), and it seems to be a more lightweight and safe list.

Dictionary dict: a key-value pair structure hash table, which has the same properties as a hash table. key is unordered and non-repeating, and addition, deletion and modification are convenient and fast.

set: An unordered and non-repeating set is a dict with only keys and no values. Java's HashSet is implemented using HashMap. I hope Python will not be like this. After all, set does not require value, so it is omitted. Lots of pointers.

Generator:

Called generator, or list comprehension, is a special data type# in python ##, is not actually a data structure, it only includes the algorithm and temporary status , and has the function of iteration.

First look at their memory usage, and use generators to generate set, dict, generator, tuple, and list of 100,000 elements. The memory consumed by dict, set, list, and tuple decreases in sequence, and the size of the generated objects is also the same. Since the generator does not generate a data table, there is no need to consume memory:

import sys
from memory_profiler import profile

@profile
def create_data(data_size):
    data_generator = (x for x in xrange(data_size))
    data_set = {x for x in xrange(data_size)}
    data_dict = {x:None for x in xrange(data_size)}
    data_tuple = tuple(x for x in xrange(data_size))
    data_list = [x for x in xrange(data_size)]
    return data_set, data_dict, data_generator, data_tuple, data_list

data_size = 100000
for data in create_data(data_size):
    print data.__class__, sys.getsizeof(data)

Line #    Mem usage    Increment   Line Contents
================================================
    14.6 MiB      0.0 MiB   @profile
                            def create_data(data_size):
    14.7 MiB      0.0 MiB       data_generator = (x for x in xrange(data_size))
    21.4 MiB      6.7 MiB       data_set = {x for x in xrange(data_size)}
    29.8 MiB      8.5 MiB       data_dict = {x:None for x in xrange(data_size)}
    33.4 MiB      3.6 MiB       data_tuple = tuple(x for x in xrange(data_size))
    38.2 MiB      4.8 MiB       data_list = [x for x in xrange(data_size)]
    38.2 MiB      0.0 MiB       return data_set, data_dict, data_generator, data_tuple, data_list
 
<type &#39;set&#39;> 4194528
<type &#39;dict&#39;> 6291728
<type &#39;generator&#39;> 72
<type &#39;tuple&#39;> 800048
<type &#39;list&#39;> 824464

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Let’s look at the search performance again. dict and set are constant search times (O(1)), and list and tuple are linear search times (O (n)), use the generator to generate an object of specified size elements, and use randomly generated numbers to find:

import time
import sys
import random
from memory_profiler import profile

def create_data(data_size):
    data_set = {x for x in xrange(data_size)}
    data_dict = {x:None for x in xrange(data_size)}
    data_tuple = tuple(x for x in xrange(data_size))
    data_list = [x for x in xrange(data_size)]
    return data_set, data_dict, data_tuple, data_list

def cost_time(func):
    def cost(*args, **kwargs):
        start = time.time()
        r = func(*args, **kwargs)
        cost = time.time() - start
        print &#39;find in %s cost time %s&#39; % (r, cost)
        return r, cost  #返回数据的类型和方法执行消耗的时间
    return cost

@cost_time
def test_find(test_data, data):
    for d in test_data:
        if d in data:
            pass
    return data.__class__.__name__

data_size = 100
test_size = 10000000
test_data = [random.randint(0, data_size) for x in xrange(test_size)]
#print test_data
for data in create_data(data_size):
    test_find(test_data, data)

输出：
----------------------------------------------
find in <type &#39;set&#39;> cost time 0.47200012207
find in <type &#39;dict&#39;> cost time 0.429999828339
find in <type &#39;tuple&#39;> cost time 5.36500000954
find in <type &#39;list&#39;> cost time 5.53399991989

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A collection of 100 elements, each searched 1000W times, and the difference is very obvious. However, these random numbers can all be found in the collection. Modify the random number method so that half of the generated numbers can be found and half cannot be found. It can be seen from the printed information that list and tuple perform even worse when there are half of the worst search examples.

def randint(index, data_size):
    return random.randint(0, data_size) if (x % 2) == 0 else random.randint(data_size, data_size * 2)

test_data = [randint(x, data_size) for x in xrange(test_size)]

输出：
----------------------------------------------
find in <type &#39;set&#39;> cost time 0.450000047684
find in <type &#39;dict&#39;> cost time 0.397000074387
find in <type &#39;tuple&#39;> cost time 7.83299994469
find in <type &#39;list&#39;> cost time 8.27800011635

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The number of elements increases from 10 to 500. Statistics of the time required to search 100,000 times each time are used to fit the time consumption curve. The results are as shown below. The results prove that no matter how many elements there are in dict and set, they are always It is a constant search time. As the elements grow, dict and tuple show a linear growth time:

import matplotlib.pyplot as plot
from numpy import *

data_size = array([x for x in xrange(10, 500, 10)])
test_size = 100000
cost_result = {}
for size in data_size:
    test_data = [randint(x, size) for x in xrange(test_size)]
    for data in create_data(size):
        name, cost = test_find(test_data, data) #装饰器函数返回函数的执行时间
        cost_result.setdefault(name, []).append(cost)

plot.figure(figsize=(10, 6))
xline = data_size
for data_type, result in cost_result.items():
    yline = array(result)
    plot.plot(xline, yline, label=data_type)

plot.ylabel(&#39;Time spend&#39;)
plot.xlabel(&#39;Find times&#39;)

plot.grid()

plot.legend()
plot.show()

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