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Понимание списка-это элегантный способ определения и создания списка на python. Мы можем создавать списки точно так же, как математические утверждения, и только в одной строке. Синтаксис понимания списка легче понять.

Понимание списка обычно состоит из этих частей:

1. Выходное выражение,
2. Последовательность ввода,
3. Переменная, представляющая элемент входной последовательности, и
4. Необязательная часть предиката.

For example :

lst  =  [x ** 2  for x in range (1, 11)   if  x % 2 == 1] 

here, x ** 2 is output expression, 
      range (1, 11)  is input sequence, 
      x is variable and   
      if x % 2 == 1 is predicate part.

Пример 1:

# Python program to demonstrate list comprehension in Python

# below list contains square of all odd numbers from
# range 1 to 10
odd_square = [x ** 2 for x in range(1, 11) if x % 2 == 1]
print (odd_square)

# for understanding, above generation is same as,
odd_square = []
for x in range(1, 11):
	if x % 2 == 1:
		odd_square.append(x**2)
print (odd_square)

# below list contains power of 2 from 1 to 8
power_of_2 = [2 ** x for x in range(1, 9)]
print (power_of_2)

# below list contains prime and non-prime in range 1 to 50
noprimes = [j for i in range(2, 8) for j in range(i*2, 50, i)]
primes = [x for x in range(2, 50) if x not in noprimes]
print (primes)

# list for lowering the characters
print ([x.lower() for x in ["A","B","C"]] )

# list which extracts number
string = "my phone number is : 11122 !!"

print("\nExtracted digits")
numbers = [x for x in string if x.isdigit()]
print (numbers)

# A list of list for multiplication table
a = 5
table = [[a, b, a * b] for b in range(1, 11)]

print("\nMultiplication Table")
for i in table:
	print (i)

Выход:

[1, 9, 25, 49, 81]
[1, 9, 25, 49, 81]
[2, 4, 8, 16, 32, 64, 128, 256]
[2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47]
['a', 'b', 'c']

Extracted digits
['1', '1', '1', '2', '2']

Multiplication Table
[5, 1, 5]
[5, 2, 10]
[5, 3, 15]
[5, 4, 20]
[5, 5, 25]
[5, 6, 30]
[5, 7, 35]
[5, 8, 40]
[5, 9, 45]
[5, 10, 50]

После получения списка мы можем получить его часть, используя оператор нарезки python, который имеет следующий синтаксис:

[start : stop : steps]  

which means that slicing will start from index start
 will go up to stop in step of steps. 
 Default value of start is 0, stop is last index of list
 and for step it is 1 

Пример 2:

# Let us first create a list to demonstrate slicing
# lst contains all number from 1 to 10
lst =list(range(1, 11))
print (lst)
	
# below list has numbers from 2 to 5
lst1_5 = lst[1 : 5]
print (lst1_5)
	
# below list has numbers from 6 to 8
lst5_8 = lst[5 : 8]
print (lst5_8)
	
# below list has numbers from 2 to 10
lst1_ = lst[1 : ]
print (lst1_)
	
# below list has numbers from 1 to 5
lst_5 = lst[: 5]
print (lst_5)
	
# below list has numbers from 2 to 8 in step 2
lst1_8_2 = lst[1 : 8 : 2]
print (lst1_8_2)
	
# below list has numbers from 10 to 1
lst_rev = lst[ : : -1]
print (lst_rev)
	
# below list has numbers from 10 to 6 in step 2
lst_rev_9_5_2 = lst[9 : 4 : -2]
print (lst_rev_9_5_2)

Выход:

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
[2, 3, 4, 5]
[6, 7, 8]
[2, 3, 4, 5, 6, 7, 8, 9, 10]
[1, 2, 3, 4, 5]
[2, 4, 6, 8]
[10, 9, 8, 7, 6, 5, 4, 3, 2, 1]
[10, 8, 6]

Мы можем использовать функцию фильтра для фильтрации списка на основе некоторого условия, представленного в виде лямбда-выражения в качестве первого аргумента и списка в качестве второго аргумента, пример которого показан ниже :

Пример 3:  

import functools

# filtering odd numbers
lst = filter(lambda x : x % 2 == 1, range(1, 20))
print (list(lst))
	
# filtering odd square which are divisible by 5
lst = filter(lambda x : x % 5 == 0,
	[x ** 2 for x in range(1, 11) if x % 2 == 1])
print (list(lst))
	
# filtering negative numbers
lst = filter((lambda x: x < 0), range(-5,5))
print (list(lst))
	
# implementing max() function, using
print (functools.reduce(lambda a,b: a if (a > b) else b, [7, 12, 45, 100, 15]))

Выход:

[1, 3, 5, 7, 9, 11, 13, 15, 17, 19]
[25]
[-5, -4, -3, -2, -1]
100