Python Loop Nesting

The Python language allows you to embed another loop inside a loop body.

Python for loop nesting syntax:

For Iterating_var in sequence:

For Iterating_var in sequence:

Statements (s)

Statements (s)

Python while loop nesting syntax:

While expression:

While expression:

Statement (s)

Statement (s)

You can embed another loop body in the loop, such as a For loop in the while loop, and conversely, you can embed a while loop in a for loop.

Instance:

1. Remove one from the first list, one at a time from the second list, combined into a new list, with all the combinations in the new list

List1 = [' Zi ', ' Qiang ', ' Xue ', ' Tang ']

List2 = [1, 2]

New_list = []

For M in List1:

For N in List2:

New_list.append ([M, N])

Print New_list

Results:

[[' Zi ', 1], [' Zi ', 2], [' Qiang ', 1], [' Qiang ', ' 2], [' Xue ', 1], [' Xue ', 2], [' Tang ', 1], [' [' Tang '], ' 2] '

2. Remove two from a list to find all combinations

List = [1, 2, 3, 4, 5]

length = Len (List)

For x in range (0, length-1):

For y in range (x+1, length):

Print list[x], list[y]

Results:

1 2

1 3

1 4

1 5

2 3

2 4

2 5

3 4

3 5

4 5

3. The following instance uses the prime number between the nested loop output 2~20:

Analysis: For a number n, if the number from 1 to n * * 0.5 (square root n) is divisible, then n is the number of primes.

3.1 using for to implement

#-*-Coding:utf-8-*-

n = 20

For I in range (1, N):

For j in range (2, int (i**0.5)):

If I% J = = 0:

Break

Else

Print I, ' is prime '

3.2 Using while to implement

#!/usr/bin/python

#-*-Coding:utf-8-*-

i = 2

while (I < 20):

j = 2

while (J <= (i/j)):

If not (I%J): # or write if I% J = = 0, if the meaning of divisible

Break

j = j + 1

if (J > i/j):

Print I, "is prime"

i = i + 1

Print "Good bye!"

Explanation: I% J means I divided by J after the remainder. For numbers, the Boolean value of 0 is false, the other values are true, the not (i% j) means that the condition is set when I j is 0 o'clock, meaning that when the division is divisible, the meaning is divisible.

The result of the above example output:

2 is prime

3 is prime

5 is prime

7 is prime

11 is prime

13 is prime

17 is prime

Good bye!

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