2.18 Weeks Four Notes

Day4

Iterators :

1.

LI=[11,22,33,44,55,66,77]

Count =len (LI)

Start = 0

While Count>start:

Print (Li[start])

Start +=1

With indexes, almost all languages support while

the nature of the 2.for cycle

A. Creating a special thing (iterator = iter ())

B. According to this thing, to manipulate the contents of the list Li

C. The execution iterator returns an object that contains the next method

D. One-to-one access to the values inside Li

obj = iter (LI)

While Ture:

item = obj__next__ ()

Item (item)

When you finish, you will be called stop ... ( the For loop does not cause an error because try except Exception: )

3. Summary:

A.while, index, subscript fetch data, random fetch

B.for, executes the iterator ITER, gets a pair of images--> Executes the next method of the object, in order to take

Generator (very important)

1.python in 2.7

Range, memory immediately created 0-9, if the number is large, eat memory

Xrange (Ten) no numbers in memory

For I in Xrange (10):

First time the memory loop is created i= 0

Memory is created in the second loop memory I=1

。。。。。。。。。。。。。。

Memory Nineth Cycles in memory created I=9

Print (i)

2.

Redis ——— Hash ( hash)

Monitor traffic data for www.baidu.com per session

Structure: Hash(hash)

N1 ——— K1 = v1

N2 ——— K11 = v11

Key value

Server 100G Local computer 10G

Dic.keys () # get all

3. File operation

f = open (' File.log ')

#f. Read () # will be reading the day into memory

For line in F: # __inter__ method for triggering F

Print (line) # Generator, memory consumption problem solved

Def show ():

Yield (line1)

Yield (line2)

Yield (LINE3)

My_f = Show ()

For line in My_f:

Print (line)

4.yield Keywords

－－－－－－－－－－－－－

Def show (): # function

Return 123

I = Show()

Print(i)

Output 123

－－－－－－－－－－－－－

Def show (): # Generator

Yield 123

I = Show()

Print(i)

Output generator

5. Summary:

Def show ():

Yield (line1)

Yield (line2)

Yield (LINE3)

My_f = Show ()

For line in My_f:

Print (line)

‘’’

Line1

Line2

Line3

’’’’

---running logic

1. If the function returns a special item that contains yield, the function returns a value (containing the next method; must be used with for)

2.for, the function returns a special thing, the internal execution of the iteration, if the yield is encountered , will yield after the value of the jump out of the function and remember the last

At the same time, assign the value to the for i

3. Then continue executing the function, go back to the last execution of the code, continue to execute

---Simple comprehension

1. The return value of the generator must be performed by the iterator

2.yield freezes the state, remembering where it was last executed

Decorative Device

def login (func): func= original show

def wrapper (*arg,**kwargs):

print(' before ')

ret =func (*arg,**kwargs)

print(ret)

print (' after ')

return tet

Return wrapper

Def show ()

Return ' show '

#show Memory Value show() execution function

New_show = login (show)

‘’’

Equivalent

Def new_show ():

ret = Show (*arg,**kwargs)

return ret

‘’’

－－－－－－－－

@login

Def show ()

Return ' show '

Functionally implements a nested

Recursive

Regular expressions

Basic algorithm

Common modules: JSON pickle

2.18 Weeks Four Notes