copy list and process control of the while loop

How to copy a list

1, the shallow copy: the first layer is the address list of the original full copy indiscriminately

Copy of the original list, generate a new list

 

 

 1.2 shallow copy method

list1 = [ 'Egon', 'lxx', [1,2]]

list2 = list1.copy()

2, deep copy

Wanted list two completely independent open and operating for change rather than read

 

 

 

 

 

 2.2 deep copy method

list1 = [ 'Egon', 'lxx', [1,2]]

 

import copy

list2 = copy.deepcopy(list1)

 

the difference:

When shallow copy is at the same address, it is to re-apply deep copy address, wherein a change of variable type, not both simultaneously changed

Process control loop while the two

1, the basic syntax and use cycle

while conditions:

　　Code 1

　　Code 2　

　　Code 3

print()

 

 

 

 Such as:

count = 0

while count < 5:

　　print(count)

　　count += 1

print ( 'top-level code')

 

2, the cycle of death and efficiency

count = 0

while count < 5:

　　print(count)

count = 0

while count < 5:

　　print(count)

 

while True:

　　name = input('yourr name')

　　print(name)

All of the above does not occur efficiency

while True:

　　1+1

No output has been running background

Pure calculation, there is no IO cycle of death can lead to deadly efficiency

3, cycle applications

= username 'abc' 
pwd = '123' 

    inp_name the INPUT = ( 'Please enter your account number:') 
    inp_pwd the INPUT = ( 'Please enter your password:') 

    IF username and pwd == == inp_name inp_pwd: 
        Print ( ' available for purchase ') 
    the else: 
        Print (' return Back ')

Requirements: input error, can then lose two times, not while you will need to re-enter the same procedure three times, very cumbersome, and would also like to lose but lost to the sides.

Repeat code, and the need for repeated lost

= username 'abc' 
pwd = '123' 

the while 1: 
    inp_name the INPUT = ( 'Please enter your account number:') 
    inp_pwd the INPUT = ( 'Please enter your password:') 

    IF username and pwd == == inp_name inp_pwd: 
        Print ( 'available for purchase') 
    the else: 
        Print ( 'return Back')

4, two ways to exit the loop

4.1, the conditions changed to False: does not take effect until the next cycle to determine when conditions

username = 'abc'
pwd = '123'

tag = True

Tag the while: 
　　Tag = False 

    inp_name the INPUT = ( 'Please enter your account number:') 
    inp_pwd the INPUT = ( 'Please enter your password:') 

    IF username and pwd == == inp_name inp_pwd: 
        Print ( 'is available for purchase') 
　　　　 # tag = False (after the code will be run, take effect until the determination condition for the next cycle) 
    the else: 
        Print ( 'return Back')

4.2 break, just run to break the cycle will immediately terminate this layer

username = 'abc'
pwd = '123'

True the while: 
    inp_name the INPUT = ( 'Please enter your account number:') 
    inp_pwd the INPUT = ( 'Please enter your password:') 

    IF username and pwd == == inp_name inp_pwd: 
        Print ( 'is available for purchase') 
　　　　 BREAK terminate this # layer cycle 
    the else: 
        Print ( 'return Back') 
Print ( 'End ==== ====')

That is, if if the result is True, the ending will not be printed ==== end ====, if it is False, there will be

5, while the nested loop

5.1 tag type

tag = True

while tag:

　　while tag:

　　　　while tag:

 　　　　　　tag = False

 

username = 'abc'
pwd = '123'
tag = True

Tag the while: 
    inp_name the INPUT = ( 'Please enter your account number:') 
    inp_pwd the INPUT = ( 'Please enter your password:') 

    IF username and pwd == == inp_name inp_pwd: 
        Print ( 'is available for purchase') 
　　　　　the while Tag: 
　　　　　　　　cmd = input ( 'enter command:') 
　　　　　　　　IF cmd == 'Q':

　　　　　　　　　　tag = False
　　　　　　　　else

　　　　　　　　　　print('order {x} is loading'.format(x = cmd))

    else:
        print('return back')
print('====end====')

　　

5.2 break: Each layer must be equipped with a break

while True：

　　while True:

　　　　while True:

　　　　break

　　break

break

username = 'abc'
pwd = '123'

True the while: 
    inp_name the INPUT = ( 'Please enter your account number:') 
    inp_pwd the INPUT = ( 'Please enter your password:') 

    IF username and pwd == == inp_name inp_pwd: 
        Print ( 'is available for purchase') 
　　　　　the while True: 
　　　　　　　　cmd = input ( 'enter command:') 
　　　　　　　　　　IF cmd == 'Q':

　　　　　　　　print('order {x} is loading'.format(x = cmd))
　　　　　　　　
　　　　　　　　　　break

　　　　 terminate this layer break # cycle 
    the else: 
        Print ( 'return Back') 
Print ( 'End ==== ====')

 

6, while + continue: the end of the cycle, directly into the next

Add similar code is meaningless after continue, because never run

 

 

count = 0

while count < 6:

　　if count == 4:

　　　　continue

　　print(count)

　　count +=1

7、while + else（针对break）

Code else will be included at the end of the while loop, and in the case while it does not like to be interrupted break the normal end, it will not run

while count < 6:

　　if count == 4:

　　　　break (behind the program is not running)

　　　　count += 1

　　　　continue

　　print(count)

　　count+=1

else:

　　print('...')

Applications:

username = 'abc'
pwd = '123'

count = 0
tag = True

Tag the while: 
　　IF COUNT == 3: 
　　　　BREAK 
    inp_name the INPUT = ( 'Please enter your account number:') 
    inp_pwd the INPUT = ( 'Please enter your password:') 

    IF username and pwd == == inp_name inp_pwd: 
        Print ( ' available for purchase ') 
　　　　　the while Tag: 
　　　　　　　　cmd = iNPUT (' input commands: ') 
　　　　　　　　IF cmd ==' Q ':

　　　　　　　　　　tag = False
　　　　　　　　else

　　　　　　　　　　print('order {x} is loading'.format(x = cmd))

    else:
        print('return back')
 　　　　count += 1