Use list

The following code demonstrates how to define a list 、 Use subscripts to access list elements and add and delete elements .

def main():
	list1 = [1, 3, 5, 7, 100]
    print(list1)
    list2 = ['hello'] * 5
    print(list2)
	#  Calculate the length of the list ( Element number )
	print(len(list1))
	#  Subscript ( Indexes ) operation 
	print(list1[0])
	print(list1[4])
	# print(list1[5])  # IndexError: list index out of range
	print(list1[-1])
	print(list1[-3])
	list1[2] = 300
	print(list1)
	#  Additive elements 
	list1.append(200)
	list1.insert(1, 400)
	list1 += [1000, 2000]
	print(list1)
	print(len(list1))
	#  Remove elements 
	list1.remove(3)
	if 1234 in list1:
		list1.remove(1234)
	del list1[0]
	print(list1)
	#  Empty list elements 
	list1.clear()
	print(list1)
	

if __name__ == '__main__':
	main()

Just like a string , The list can also be sliced , Through slicing, we can copy the list or take out part of the list to create a new list , The code is as follows .

def main():
	fruits = ['grape', 'apple', 'strawberry', 'waxberry']
	fruits += ['pitaya', 'pear', 'mango']
	#  Loop through list elements 
	for fruit in fruits:
		print(fruit.title(), end=' ')
	print()
	#  List slice 
	fruits2 = fruits[1:4]
	print(fruits2)
	# fruit3 = fruits  #  There is no copy list, only new references are created 
    #  You can copy the list through the full slice operation 
	fruits3 = fruits[:]
	print(fruits3)
	fruits4 = fruits[-3:-1]
	print(fruits4)
    #  You can get a copy of the inverted list by reverse slicing 
	fruits5 = fruits[::-1]
	print(fruits5)


if __name__ == '__main__':
	main()

The following code implements the sorting operation of the list .

def main():
    list1 = ['orange', 'apple', 'zoo', 'internationalization', 'blueberry']
    list2 = sorted(list1)
    # sorted The function returns the sorted copy of the list without modifying the incoming list 
    #  The design of functions should be like sorted Function, as far as possible without side effects 
    list3 = sorted(list1, reverse=True)
    #  adopt key The keyword parameter specifies to sort by string length instead of the default alphabetic order 
    list4 = sorted(list1, key=len)
    print(list1)
    print(list2)
    print(list3)
    print(list4)
    #  Send a sort message to the list object and sort directly on the list object 
    list1.sort(reverse=True)
    print(list1)


if __name__ == '__main__':
    main()

We can also use the generative syntax of lists to create lists , The code is as follows .

import sys


def main():
    f = [x for x in range(1, 10)]
    print(f)
    f = [x + y for x in 'ABCDE' for y in '1234567']
    print(f)
    #  Create a list container using the list generation expression syntax 
    #  After creating the list with this syntax, the elements are ready, so it takes a lot of memory space 
    f = [x ** 2 for x in range(1, 1000)]
    print(sys.getsizeof(f))  #  View the number of bytes of memory occupied by the object 
    print(f)
    #  Note that the following code creates not a list, but a generator object 
    #  Data can be obtained through the generator, but it does not take up additional space to store data 
    #  Every time you need data, you get the data through internal operation ( It takes extra time )
    f = (x ** 2 for x in range(1, 1000))
    print(sys.getsizeof(f))  #  Compared with the generative generator, it does not occupy the space to store data 
    print(f)
    for val in f:
        print(val)


if __name__ == '__main__':
    main()

In addition to the generator syntax mentioned above ,Python There's another way to define generators , It is through yield Keyword transforms a normal function into a generator function . The following code demonstrates how to implement a build Fiborache series The generator . The so-called fiborache sequence can be passed through the following recursive To define ：

$${\displaystyle F_{0}=0}$$

$${\displaystyle F_{1}=1}$$

$${\displaystyle F_{n}=F_{n-1}+F_{n-2}}({n}\geq{2})$$

def fib(n):
    a, b = 0, 1
    for _ in range(n):
        a, b = b, a + b
        yield a


def main():
	for val in fib(20):
	    print(val)


if __name__ == '__main__':
	main()