Learning Python:day3

1. Collection Operations

A collection is an unordered, non-repeating combination of data, and its main functions are as follows:

• Go to the weight, turn a list into a set, and then automatically go heavy.
• Relationship test, test the intersection of two sets of data, difference set, and the relationship between the set

s = set ([3,5,9,10]) #创建一个数值集合

t = Set ("Hello") #创建一个唯一字符的集合

A = T | The set of S # T and S

b = Intersection of T & S # T and S

c = t–s # differential Set (item in T, but not in s)

D = t ^ S # symmetric difference set (items in t or S, but not both)



Basic operation:

T.add (' x ') # Add an item

S.update ([10,37,42]) # Add multiple items in S



Use Remove () to delete an item:

T.remove (' H ')


Len (s)
The length of the set

X in S
Test if X is a member of S

X not in S
Test if X is not a member of S

S.issubset (t)
S <= t
Test if every element in S is in t

S.issuperset (t)
S >= t
Tests if every element in T is in S

S.union (t)
s | T
Returns a new set containing each element in S and T

S.intersection (t)
S & T
Returns a new set containing the common elements in S and T

S.difference (t)
S-t
Returns a new set containing elements in s but not in t

S.symmetric_difference (t)
s ^ t
Returns a new set containing elements that are not duplicates in S and T

S.copy ()
Returns a shallow copy of the set "s"

2. file Operations

Procedure for file operation

1. Open the file, get the file handle and assign a value to a variable
2. Manipulating a file with a handle
3. Close File

The mode of opening the file is:

• R, read-only mode (default).
• W, write-only mode. "unreadable; not exist; create; delete content;"
• A, append mode. "Readable; not exist" create; "only append content;"

"+" means you can read and write a file at the same time

• r+, can read and write files. "readable; writable; can be added"
• w+, write and read
• A +, with a

"U" means that the \ r \ n \ r \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ r or r+ mode can be converted automatically when reading

• RU
• R+u

"B" means processing binary files (e.g. FTP send upload ISO image file, Linux can be ignored, Windows process binary file should be labeled)

• Rb
• Wb
• Ab

File modification

f = open ("Yesterday2.txt", "R", encoding= "Utf-8")
f_new = open ("Yesterday2_bak.txt", "W", encoding= "Utf-8")

For line in F:
    If  "Dick and Harry" in line:
        line = Line.replace ("Dick and Harry", "Zhangsanlisi")
    F_new.write (line)
F.close ()
F_new.close ()

File read/write

f = open ("Yesterday.txt", ' r+ ', encoding= "Utf-8") #文件句柄 Encoding=utf-8
#a = Append append cannot be read, append does not overwrite W overlay
data = F.read ()
Print (data)

#f. Write ("I love Beijing Tian ' an door \ n")
#f. Write ("Taiyanghong")
#print (f)
#low的循环
‘‘‘
For Index,line in Enumerate (F.readlines ()):
    If index = = 9:
        Print ("--------fengexian------")
        Continue
    Print (Line.strip ())
    ‘‘‘
#hight
For line in F:
    Print (line)

Print (F.tell ()) #打印光标位置
F.seek (#光标重新定位)

3. Character encoding and transcoding

Detailed article: http://www.cnblogs.com/luotianshuai/articles/5735051.html

4. Function parameters and Local variables

#列表 Dictionary collection classes can be changed in local variables
Not #字符串 integer.
School = "Old boy"
def chang_name (name):
    Global School
    School = "Qinghua"
    Print ("Before Chang", name)
    Name = "Alex li" #这个函数就是这个变量的作用域
    Print ("After Chang", name)

Name = "Alex"
Chang_name (name)
Print (name)
Print ("School:", school)

---------------------------

Import time
Def logger_test ():
    Time_format = "%y-%m-%d%x"
    Time_current = Time.strftime (Time_format)
    With open (' a.txt ', ' A + ') as F:
        F.write ("%s End action \ n"%time_current)
def test1 ():
    Print ("Test1 starting action")
    Logger_test ()
Def test2 ():
    Print ("Test2 starting action")
    Logger_test ()
def test3 ():
    Print ("Test3 starting action")
    Logger_test ()
Test1 ()
Test2 ()
Test3 ()
def test4 (x, Y, z):
    Print (x)
    Print (y)
    Print (z)
Test4 (y=2,x=1,z=6)
Test4 (4,5,9)
Test4 (4,z=3,y=8)

def test5 (x,y=2):
    Print (x)
    Print (y)
TEST5 (1,3)
#默认参数特点: When calling a function, the default function must not pass
#用途: 1, default installation value
#      2, default value
#接收多个参数组成元组
#*args: Accept n Positional parameters, convert Narimoto Group
def test6 (X,*args):
    Print (x)
    Print (args)
Test6 (1,2,3,45,66,8)

---------------------------

#吧N个关键字参数写成字典, receive Key:value
def test (**kargs):
    Print (Kargs)
    Print (kargs[' name '])
    Print (kargs[' age ')
Test (name= "Alex", age= "8", sex= "F")
Test (**{' name ': ' Alex ', ' age ': ' 8 '})

def test2 (Name,**kwargs):
    Print (name)
    Print (Kwargs)
Test2 (' Alex ', age=18,sex= ' F ')

def test3 (Name,*args,**kwargs):
    Print (name)
    Print (args)
    Print (Kwargs)
Test3 (' Alex ', 2,3,4,5,age= ', sex= ' M ')
#位置参数不能放在关键字参数后

5. Recursion

Inside a function, you can call other functions. If a function calls itself internally, the function is a recursive function.

Def calc (n):
    Print (n)
    if int (N/2) > 0:
        Return calc (int (N/2))
    Print ("---", N)
Calc (10)

Learning Python:day3