10. Loop statement

   for loop statements, Python only provides while and for, not for...each/do...while/while...do, etc. like other programming languages.

10.1 while cycle

The basic format of   while in Python is as follows:

while condition:
    doSomething

The    example code is as follows:

startNum,endNum=0,5
while startNum< endNum:
    print(f"cur start number is {startNum}")
    startNum+=1

The output is as follows:

cur start number is 0
cur start number is 1
cur start number is 2
cur start number is 3
cur start number is 4

10.2 for cycle

1. Basic for cycle

The basic format of the for loop in Python is as follows:

for item in [List, tuple, dictionary, set, character, etc]: 
   doSomething

The    example code is as follows:

a={1,2,3,4,5}
for item in a:
    print(f"current item is {item}")

The output is as follows:

current item is 1
current item is 2
current item is 3
current item is 4
current item is 5

2.for..else loop

                    . The basic syntax for mat is as follows:

for item in [List, tuple, dictionary, set, character, etc]: 
   doSomething
else:
   doSomething

   sometimes we need to judge whether the program loop exits normally or midway. We can use the following code:

a = [1, 2, 3, 4]
flag = True
for i in a:
    if i == 2:
        flag = False
        break

if flag:
    print('yes')
else:
    print('no')

   for the above writing method, you can use for...else to simplify the writing method, as follows:

a = [1, 2, 3, 4]
for i in a:
    if i == 2:
        break
else:
    print('yes')

print('no')

   since Python provides two forms of loop statements, what is the difference between the two, when to use the while loop and when to use the for loop?

10.3 interrupt statement

                         

• break: interrupt the whole cycle, that is, when the conditions are met, the cycle will be stopped immediately, and subsequent cycles will not continue
• Continue: interrupt the current cycle, that is, when the conditions are met, the current cycle will be terminated, and the cycle will continue when the conditions are met later

The    example code is as follows:

print("break loop")
for i in range(6):
    if i == 3:
        break
    print(f"current value is {i}")
print("continue loop")
for i in range(6):
    if i == 3:
        continue
    print(f"current value is {i}")

The output is as follows:

break loop
current value is 0
current value is 1
current value is 2
continue loop
current value is 0
current value is 1
current value is 2
current value is 4
current value is 5

10.4 traversing container data

1.range() function

The    range() function is commonly used to generate a series of numbers. Its basic usage format is as follows:

range(start,end,step)

• Start: start value
• End: end value
• Step: step, which can be positive, negative or omitted. When omitted, the default step is 1
• Use the range() function to generate data, and also follow the rule of "before and after", such as range(0,3). The generated data is 0,1,2

The    example code is as follows:

list(range(0,10,2))
# Output results
[0, 2, 4, 6, 8]

list(range(10,0,-2))
# Output results
[10, 8, 6, 4, 2]

2. Traverse string data

                      

for i in "abcdef":
    print(f"current char is {i}")

The output is as follows:

current char is a
current char is b
current char is c
current char is d
current char is e
current char is f

3. Traversal tuple

The    example code is as follows:

for i in tuple(range(0,5)):
    print(f"current value is {i}")

The output is as follows:

current value is 0
current value is 1
current value is 2
current value is 3
current value is 4

4. Traversal list

The    example code is as follows:

for i in list(range(0,5)):
    print(f"current value is {i}")

The output is as follows:

current value is 0
current value is 1
current value is 2
current value is 3
current value is 4

5. Traversal set

The    example code is as follows:

for i in set(range(0,5)):
    print(f"current value is {i}")

The output is as follows:

current value is 0
current value is 1
current value is 2
current value is 3
current value is 4

6. Traversal dictionary
The    example code is as follows:

dic={
    "a":1,
    "b":2,
    "c":3,
    "d":4,
}

for k,v in dic.items():
    print(f"key is {k} , value is {v}")

The output is as follows:

key is a , value is 1
key is b , value is 2
key is c , value is 3
key is d , value is 4

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